diff --git includes/menu.inc includes/menu.inc
index 38e4f77..990dfdc 100644
--- includes/menu.inc
+++ includes/menu.inc
@@ -1115,6 +1115,47 @@ function menu_tree_all_data($menu_name, $link = NULL, $max_depth = NULL) {
 }
 
 /**
+ * Set the path for determining the active trail of the specified menu tree.
+ *
+ * This path will also affect the breadcrumbs under some circumstances.
+ * Breadcrumbs are built using the preferred link returned by
+ * menu_link_get_preferred(). If the preferred link is inside one of the menus
+ * specified in calls to menu_tree_set_path(), the preferred link will be
+ * overridden by the corresponding path returned by menu_tree_get_path().
+ *
+ * Setting this path does not affect the main content; for that use
+ * menu_set_active_item() instead.
+ *
+ * @param $menu_name
+ *   The name of the affected menu tree.
+ * @param $path
+ *   The path to use when finding the active trail.
+ */
+function menu_tree_set_path($menu_name, $path) {
+  return menu_tree_get_path($menu_name, $path);
+}
+
+/**
+ * Get the path for determining the active trail of the specified menu tree.
+ *
+ * @param $menu_name
+ *   The menu name of the requested tree.
+ * @param $path
+ *   Internal use only.
+ *
+ * @return
+ *   A string containing the path. If no path has been specified with
+ *   menu_tree_set_path(), NULL is returned.
+ */
+function menu_tree_get_path($menu_name, $path = NULL) {
+  $paths = &drupal_static(__FUNCTION__);
+  if (isset($path)) {
+    $paths[$menu_name] = $path;
+  }
+  return isset($paths[$menu_name]) ? $paths[$menu_name] : NULL;
+}
+
+/**
  * Get the data structure representing a named menu tree, based on the current page.
  *
  * The tree order is maintained by storing each parent in an individual
@@ -1139,8 +1180,10 @@ function menu_tree_all_data($menu_name, $link = NULL, $max_depth = NULL) {
 function menu_tree_page_data($menu_name, $max_depth = NULL, $only_active_trail = FALSE) {
   $tree = &drupal_static(__FUNCTION__, array());
 
+  // Check if the active trail has been overridden for this menu tree.
+  $active_path = menu_tree_get_path($menu_name);
   // Load the menu item corresponding to the current page.
-  if ($item = menu_get_item()) {
+  if ($item = menu_get_item($active_path)) {
     if (isset($max_depth)) {
       $max_depth = min($max_depth, MENU_MAX_DEPTH);
     }
@@ -1179,8 +1222,9 @@ function menu_tree_page_data($menu_name, $max_depth = NULL, $only_active_trail =
         // If the item for the current page is accessible, build the tree
         // parameters accordingly.
         if ($item['access']) {
-          // Find a menu link corresponding to the current path.
-          if ($active_link = menu_link_get_preferred()) {
+          // Find a menu link corresponding to the current path. If $active_path
+          // is NULL, let menu_link_get_preferred() determine the path.
+          if ($active_link = menu_link_get_preferred($active_path)) {
             // The active link may only be taken into account to build the
             // active trail, if it resides in the requested menu. Otherwise,
             // we'd needlessly re-run _menu_build_tree() queries for every menu
@@ -2210,38 +2254,36 @@ function menu_get_active_menu_names() {
 /**
  * Set the active path, which determines which page is loaded.
  *
- * @param $path
- *   A Drupal path - not a path alias.
- *
  * Note that this may not have the desired effect unless invoked very early
  * in the page load, such as during hook_boot, or unless you call
  * menu_execute_active_handler() to generate your page output.
+ *
+ * @param $path
+ *   A Drupal path - not a path alias.
  */
 function menu_set_active_item($path) {
   $_GET['q'] = $path;
 }
 
 /**
- * Sets or gets the active trail (path to menu tree root) of the current page.
+ * Sets the active trail (path to menu tree root) of the current page.
+ *
+ * Any trail set by this function will only be used for functionality that calls
+ * menu_get_active_trail(). Drupal core only uses trails set here for
+ * breadcrumbs and the page title and not for menu trees or page content.
+ * Additionally, breadcrumbs set by drupal_set_breadcrumb() will override any
+ * trail set here.
+ *
+ * To affect the trail used by menu trees, use menu_tree_set_path(). To affect
+ * the page content, use menu_set_active_item() instead.
  *
  * @param $new_trail
- *   Menu trail to set, or NULL to use previously-set or calculated trail. If
- *   supplying a trail, use the same format as the return value (see below).
+ *   Menu trail to set; the value is saved in a static variable and can be
+ *   retrieved by menu_get_active_trail(). The format of this array should be
+ *   the same as the return value of menu_get_active_trail().
  *
  * @return
- *   Path to menu root of the current page, as an array of menu link items,
- *   starting with the site's home page. Each link item is an associative array
- *   with the following components:
- *   - title: Title of the item.
- *   - href: Drupal path of the item.
- *   - localized_options: Options for passing into the l() function.
- *   - type: A menu type constant, such as MENU_DEFAULT_LOCAL_TASK, or 0 to
- *     indicate it's not really in the menu (used for the home page item).
- *   If $new_trail is supplied, the value is saved in a static variable and
- *   returned. If $new_trail is not supplied, and there is a saved value from
- *   a previous call, the saved value is returned. If $new_trail is not supplied
- *   and there is no saved value, the path to the current page is calculated,
- *   saved as the static value, and returned.
+ *   The active trail. See menu_get_active_trail() for details.
  */
 function menu_set_active_trail($new_trail = NULL) {
   $trail = &drupal_static(__FUNCTION__);
@@ -2398,7 +2440,20 @@ function menu_link_get_preferred($path = NULL) {
 /**
  * Gets the active trail (path to root menu root) of the current page.
  *
- * See menu_set_active_trail() for details of return value.
+ * If a trail is supplied to menu_set_active_trail(), that value is returned. If
+ * a trail is not supplied to menu_set_active_trail(), the path to the current
+ * page is calculated and returned. The calculated trail is also saved as a
+ * static value for use by subsequent calls to menu_get_active_trail().
+ *
+ * @return
+ *   Path to menu root of the current page, as an array of menu link items,
+ *   starting with the site's home page. Each link item is an associative array
+ *   with the following components:
+ *   - title: Title of the item.
+ *   - href: Drupal path of the item.
+ *   - localized_options: Options for passing into the l() function.
+ *   - type: A menu type constant, such as MENU_DEFAULT_LOCAL_TASK, or 0 to
+ *     indicate it's not really in the menu (used for the home page item).
  */
 function menu_get_active_trail() {
   return menu_set_active_trail();
diff --git modules/simpletest/tests/menu.test modules/simpletest/tests/menu.test
index acbd7c8..1fbba7b 100644
--- modules/simpletest/tests/menu.test
+++ modules/simpletest/tests/menu.test
@@ -6,6 +6,118 @@
  * Provides SimpleTests for menu.inc.
  */
 
+class MenuWebTestCase extends DrupalWebTestCase {
+  function setUp($modules = array()) {
+    parent::setUp($modules);
+  }
+
+  /**
+   * Assert that a given path shows certain breadcrumb links.
+   *
+   * @param string $goto
+   *   (optional) A system path to pass to DrupalWebTestCase::drupalGet().
+   * @param array $trail
+   *   An associative array whose keys are expected breadcrumb link paths and
+   *   whose values are expected breadcrumb link texts (not sanitized).
+   * @param string $page_title
+   *   (optional) A page title to additionally assert via
+   *   DrupalWebTestCase::assertTitle(). Without site name suffix.
+   * @param array $tree
+   *   (optional) An associative array whose keys are link paths and whose
+   *   values are link titles (not sanitized) of an expected active trail in a
+   *   menu tree output on the page.
+   * @param $last_active
+   *   (optional) Whether the last link in $tree is expected to be active (TRUE)
+   *   or just to be in the active trail (FALSE).
+   */
+  protected function assertBreadcrumb($goto, array $trail, $page_title = NULL, array $tree = array(), $last_active = TRUE) {
+    if (isset($goto)) {
+      $this->drupalGet($goto);
+    }
+    // Compare paths with actual breadcrumb.
+    $parts = $this->getParts();
+    $pass = TRUE;
+    foreach ($trail as $path => $title) {
+      $url = url($path);
+      $part = array_shift($parts);
+      $pass = ($pass && $part['href'] === $url && $part['text'] === check_plain($title));
+    }
+    // No parts must be left, or an expected "Home" will always pass.
+    $pass = ($pass && empty($parts));
+
+    $this->assertTrue($pass, t('Breadcrumb %parts found on @path.', array(
+      '%parts' => implode(' » ', $trail),
+      '@path' => $this->getUrl(),
+    )));
+
+    // Additionally assert page title, if given.
+    if (isset($page_title)) {
+      $this->assertTitle(strtr('@title | Drupal', array('@title' => $page_title)));
+    }
+
+    // Additionally assert active trail in a menu tree output, if given.
+    if ($tree) {
+      end($tree);
+      $active_link_path = key($tree);
+      $active_link_title = array_pop($tree);
+      $xpath = '';
+      if ($tree) {
+        $i = 0;
+        foreach ($tree as $link_path => $link_title) {
+          $part_xpath = (!$i ? '//' : '/following-sibling::ul/descendant::');
+          $part_xpath .= 'li[contains(@class, :class)]/a[contains(@href, :href) and contains(text(), :title)]';
+          $part_args = array(
+            ':class' => 'active-trail',
+            ':href' => url($link_path),
+            ':title' => $link_title,
+          );
+          $xpath .= $this->buildXPathQuery($part_xpath, $part_args);
+          $i++;
+        }
+        $elements = $this->xpath($xpath);
+        $this->assertTrue(!empty($elements), t('Active trail to current page was found in menu tree.'));
+
+        // Append prefix for active link asserted below.
+        $xpath .= '/following-sibling::ul/descendant::';
+      }
+      else {
+        $xpath .= '//';
+      }
+      $xpath_last_active = ($last_active ? 'and contains(@class, :class-active)' : '');
+      $xpath .= 'li[contains(@class, :class-trail)]/a[contains(@href, :href) ' . $xpath_last_active . 'and contains(text(), :title)]';
+      $args = array(
+        ':class-trail' => 'active-trail',
+        ':class-active' => 'active',
+        ':href' => url($active_link_path),
+        ':title' => $active_link_title,
+      );
+      $elements = $this->xpath($xpath, $args);
+      $this->assertTrue(!empty($elements), t('Active link %title was found in menu tree, including active trail links %tree.', array(
+        '%title' => $active_link_title,
+        '%tree' => implode(' » ', $tree),
+      )));
+    }
+  }
+
+  /**
+   * Returns the breadcrumb contents of the current page in the internal browser.
+   */
+  protected function getParts() {
+    $parts = array();
+    $elements = $this->xpath('//div[@class="breadcrumb"]/a');
+    if (!empty($elements)) {
+      foreach ($elements as $element) {
+        $parts[] = array(
+          'text' => (string) $element,
+          'href' => (string) $element['href'],
+          'title' => (string) $element['title'],
+        );
+      }
+    }
+    return $parts;
+  }
+}
+
 class MenuRouterTestCase extends DrupalWebTestCase {
   public static function getInfo() {
     return array(
@@ -806,7 +918,7 @@ class MenuTreeDataTestCase extends DrupalUnitTestCase {
 /**
  * Menu breadcrumbs related tests.
  */
-class MenuBreadcrumbTestCase extends DrupalWebTestCase {
+class MenuBreadcrumbTestCase extends MenuWebTestCase {
   public static function getInfo() {
     return array(
       'name' => 'Breadcrumbs',
@@ -1291,110 +1403,112 @@ class MenuBreadcrumbTestCase extends DrupalWebTestCase {
     $this->assertBreadcrumb('admin/reports/dblog', $trail, t('Recent log messages'));
     $this->assertNoResponse(403);
   }
+}
 
-  /**
-   * Assert that a given path shows certain breadcrumb links.
-   *
-   * @param string $goto
-   *   (optional) A system path to pass to DrupalWebTestCase::drupalGet().
-   * @param array $trail
-   *   An associative array whose keys are expected breadcrumb link paths and
-   *   whose values are expected breadcrumb link texts (not sanitized).
-   * @param string $page_title
-   *   (optional) A page title to additionally assert via
-   *   DrupalWebTestCase::assertTitle(). Without site name suffix.
-   * @param array $tree
-   *   (optional) An associative array whose keys are link paths and whose
-   *   values are link titles (not sanitized) of an expected active trail in a
-   *   menu tree output on the page.
-   * @param $last_active
-   *   (optional) Whether the last link in $tree is expected to be active (TRUE)
-   *   or just to be in the active trail (FALSE).
-   */
-  protected function assertBreadcrumb($goto, array $trail, $page_title = NULL, array $tree = array(), $last_active = TRUE) {
-    if (isset($goto)) {
-      $this->drupalGet($goto);
-    }
-    // Compare paths with actual breadcrumb.
-    $parts = $this->getParts();
-    $pass = TRUE;
-    foreach ($trail as $path => $title) {
-      $url = url($path);
-      $part = array_shift($parts);
-      $pass = ($pass && $part['href'] === $url && $part['text'] === check_plain($title));
-    }
-    // No parts must be left, or an expected "Home" will always pass.
-    $pass = ($pass && empty($parts));
-
-    $this->assertTrue($pass, t('Breadcrumb %parts found on @path.', array(
-      '%parts' => implode(' » ', $trail),
-      '@path' => $this->getUrl(),
-    )));
+/**
+ * Tests active menu trails.
+ */
+class MenuTrailTestCase extends MenuWebTestCase {
+  public static function getInfo() {
+    return array(
+      'name' => 'Active trail',
+      'description' => 'Tests active menu trails and alteration functionality.',
+      'group' => 'Menu',
+    );
+  }
 
-    // Additionally assert page title, if given.
-    if (isset($page_title)) {
-      $this->assertTitle(strtr('@title | Drupal', array('@title' => $page_title)));
-    }
+  function setUp() {
+    parent::setUp(array('menu_test'));
+    $this->admin_user = $this->drupalCreateUser(array('administer site configuration', 'access administration pages'));
+    $this->drupalLogin($this->admin_user);
 
-    // Additionally assert active trail in a menu tree output, if given.
-    if ($tree) {
-      end($tree);
-      $active_link_path = key($tree);
-      $active_link_title = array_pop($tree);
-      $xpath = '';
-      if ($tree) {
-        $i = 0;
-        foreach ($tree as $link_path => $link_title) {
-          $part_xpath = (!$i ? '//' : '/following-sibling::ul/descendant::');
-          $part_xpath .= 'li[contains(@class, :class)]/a[contains(@href, :href) and contains(text(), :title)]';
-          $part_args = array(
-            ':class' => 'active-trail',
-            ':href' => url($link_path),
-            ':title' => $link_title,
-          );
-          $xpath .= $this->buildXPathQuery($part_xpath, $part_args);
-          $i++;
-        }
-        $elements = $this->xpath($xpath);
-        $this->assertTrue(!empty($elements), t('Active trail to current page was found in menu tree.'));
+    // This test puts menu links in the Navigation menu and then tests for
+    // their presence on the page, so we need to ensure that the Navigation
+    // block will be displayed in all active themes.
+    db_update('block')
+      ->fields(array(
+        // Use a region that is valid for all themes.
+        'region' => 'content',
+        'status' => 1,
+      ))
+      ->condition('module', 'system')
+      ->condition('delta', 'navigation')
+      ->execute();
 
-        // Append prefix for active link asserted below.
-        $xpath .= '/following-sibling::ul/descendant::';
-      }
-      else {
-        $xpath .= '//';
-      }
-      $xpath_last_active = ($last_active ? 'and contains(@class, :class-active)' : '');
-      $xpath .= 'li[contains(@class, :class-trail)]/a[contains(@href, :href) ' . $xpath_last_active . 'and contains(text(), :title)]';
-      $args = array(
-        ':class-trail' => 'active-trail',
-        ':class-active' => 'active',
-        ':href' => url($active_link_path),
-        ':title' => $active_link_title,
-      );
-      $elements = $this->xpath($xpath, $args);
-      $this->assertTrue(!empty($elements), t('Active link %title was found in menu tree, including active trail links %tree.', array(
-        '%title' => $active_link_title,
-        '%tree' => implode(' » ', $tree),
-      )));
-    }
+    // This test puts menu links in the Management menu and then tests for
+    // their presence on the page, so we need to ensure that the Management
+    // block will be displayed in all active themes.
+    db_update('block')
+      ->fields(array(
+        // Use a region that is valid for all themes.
+        'region' => 'content',
+        'status' => 1,
+      ))
+      ->condition('module', 'system')
+      ->condition('delta', 'management')
+      ->execute();
   }
 
   /**
-   * Returns the breadcrumb contents of the current page in the internal browser.
+   * Tests active trails are properly affected by menu_tree_set_path().
    */
-  protected function getParts() {
-    $parts = array();
-    $elements = $this->xpath('//div[@class="breadcrumb"]/a');
-    if (!empty($elements)) {
-      foreach ($elements as $element) {
-        $parts[] = array(
-          'text' => (string) $element,
-          'href' => (string) $element['href'],
-          'title' => (string) $element['title'],
-        );
-      }
-    }
-    return $parts;
+  function testMenuTreeSetPath() {
+    $home = array('<front>' => 'Home');
+    $config_tree = array(
+      'admin' => t('Administration'),
+      'admin/config' => t('Configuration'),
+    );
+    $config = $home + $config_tree;
+
+    // The menu_test_menu_tree_set_path system variable controls whether or not
+    // the menu_test_menu_trail_callback() callback (used by all paths in these
+    // tests) issues an overriding call to menu_trail_set_path().
+    $test_menu_path = array(
+      'menu_name' => 'management',
+      'path' => 'admin/config/system/site-information',
+    );
+
+    $breadcrumb = $home + array(
+      'menu-test' => t('Menu test root'),
+    );
+    $tree = array(
+      'menu-test' => t('Menu test root'),
+      'menu-test/menu-trail' => t('Menu trail - Case 1'),
+    );
+
+    // Test the tree generation for the Navigation menu.
+    variable_del('menu_test_menu_tree_set_path');
+    $this->assertBreadcrumb('menu-test/menu-trail', $breadcrumb, t('Menu trail - Case 1'), $tree);
+
+    // Override the active trail for the Management tree; it should not affect
+    // the Navigation tree.
+    variable_set('menu_test_menu_tree_set_path', $test_menu_path);
+    $this->assertBreadcrumb('menu-test/menu-trail', $breadcrumb, t('Menu trail - Case 1'), $tree);
+
+    $breadcrumb = $config + array(
+      'admin/config/development' => t('Development'),
+    );
+    $tree = $config_tree + array(
+      'admin/config/development' => t('Development'),
+      'admin/config/development/menu-trail' => t('Menu trail - Case 2'),
+    );
+
+    $override_breadcrumb = $config + array(
+      'admin/config/system' => t('System'),
+      'admin/config/system/site-information' => t('Site information'),
+    );
+    $override_tree = $config_tree + array(
+      'admin/config/system' => t('System'),
+      'admin/config/system/site-information' => t('Site information'),
+    );
+
+    // Test the tree generation for the Management menu.
+    variable_del('menu_test_menu_tree_set_path');
+    $this->assertBreadcrumb('admin/config/development/menu-trail', $breadcrumb, t('Menu trail - Case 2'), $tree);
+
+    // Override the active trail for the Management tree; it should affect the
+    // breadcrumbs and Management tree.
+    variable_set('menu_test_menu_tree_set_path', $test_menu_path);
+    $this->assertBreadcrumb('admin/config/development/menu-trail', $override_breadcrumb, t('Menu trail - Case 2'), $override_tree);
   }
 }
diff --git modules/simpletest/tests/menu_test.module modules/simpletest/tests/menu_test.module
index 4c38502..9480e82 100644
--- modules/simpletest/tests/menu_test.module
+++ modules/simpletest/tests/menu_test.module
@@ -211,6 +211,20 @@ function menu_test_menu() {
     'type' => MENU_LOCAL_TASK,
   ) + $base;
 
+  // Menu trail tests.
+  // @see MenuTrailTestCase
+  $items['menu-test/menu-trail'] = array(
+    'title' => 'Menu trail - Case 1',
+    'page callback' => 'menu_test_menu_trail_callback',
+    'access arguments' => array('access content'),
+  );
+  $items['admin/config/development/menu-trail'] = array(
+    'title' => 'Menu trail - Case 2',
+    'description' => 'Tests menu_tree_set_path()',
+    'page callback' => 'menu_test_menu_trail_callback',
+    'access arguments' => array('access administration pages'),
+  );
+
   // File inheritance tests. This menu item should inherit the page callback
   // system_admin_menu_block_page() and therefore render its children as links
   // on the page.
@@ -325,6 +339,17 @@ function menu_test_callback() {
 }
 
 /**
+ * Callback that test menu_test_menu_tree_set_path().
+ */
+function menu_test_menu_trail_callback() {
+  $menu_path = variable_get('menu_test_menu_tree_set_path', array());
+  if (!empty($menu_path)) {
+    menu_tree_set_path($menu_path['menu_name'], $menu_path['path']);
+  }
+  return 'This is menu_test_menu_trail_callback().';
+}
+
+/**
  * Page callback to use when testing the theme callback functionality.
  *
  * @param $inherited