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..fff8279 100644
--- modules/simpletest/tests/menu.test
+++ modules/simpletest/tests/menu.test
@@ -1398,3 +1398,122 @@ class MenuBreadcrumbTestCase extends DrupalWebTestCase {
     return $parts;
   }
 }
+
+/**
+ * Active menu trail related tests.
+ */
+class MenuTrailTestCase extends MenuBreadcrumbTestCase {
+  public static function getInfo() {
+    return array(
+      'name' => 'Menu trail display',
+      'description' => 'Tests menu trail display and alteration functions.',
+      'group' => 'Menu',
+    );
+  }
+
+  function setUp() {
+    parent::setUp();
+
+    // 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();
+  }
+
+  /**
+   * Prevents parent class' tests from running.
+   */
+  function testBreadCrumbs() {
+  }
+
+  /**
+   * Tests active trails are properly affected by menu_tree_set_path().
+   */
+  function testMenuTreeSetPath() {
+    $home = array('<front>' => 'Home');
+    $config = $home + array(
+      'admin' => t('Administration'),
+      'admin/config' => t('Configuration'),
+    );
+
+    // 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 overrding call to menu_trail_set_path().
+    $test_menu_path = array(
+      'menu_name' => 'management',
+      'path' => 'admin/config/system/site-information',
+    );
+
+    $case1_breadcrumb = $home + array(
+      'menu-test' => t('Menu test root'),
+    );
+    $case1_tree = array(
+      'menu-test' => t('Menu test root'),
+      'menu-test/menu-trail' => t('Menu trail - Case 1'),
+    );
+
+    $case2_breadcrumb = $config + array(
+      'admin/config/development' => t('Development'),
+    );
+    $case2_tree = $case2_breadcrumb + array(
+      'admin/config/development/menu-trail' => t('Menu trail - Case 2'),
+    );
+    array_shift($case2_tree); // Remove the Home link from the tree array.
+
+    $case2_override_breadcrumb = $config + array(
+      'admin/config/system' => t('System'),
+      'admin/config/system/site-information' => t('Site information'),
+    );
+    $case2_override_tree = $case2_override_breadcrumb;
+    array_shift($case2_override_tree); // Remove the Home link from the tree array.
+
+    // Test the tree generation for the Navigation menu.
+    variable_del('menu_test_menu_tree_set_path');
+    $this->assertTrail('menu-test/menu-trail', $case1_breadcrumb, t('Menu trail - Case 1'), $case1_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->assertTrail('menu-test/menu-trail', $case1_breadcrumb, t('Menu trail - Case 1'), $case1_tree);
+
+    // Test the tree generation for the Management menu.
+    variable_del('menu_test_menu_tree_set_path');
+    $this->assertTrail('admin/config/development/menu-trail', $case2_breadcrumb, t('Menu trail - Case 2'), $case2_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->assertTrail('admin/config/development/menu-trail', $case2_override_breadcrumb, t('Menu trail - Case 2'), $case2_override_tree);
+  }
+
+  /**
+   * Assert that a given path shows certain breadcrumb links.
+   *
+   * @param string $goto
+   *   (optional) A system path to pass to DrupalWebTestCase::drupalGet().
+   * @param array $breadcrumb
+   *   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 array $last_active
+   *   (optional) Whether the last link in $tree is expected to be active (TRUE)
+   *   or just to be in the active trail (FALSE).
+   */
+  protected function assertTrail($goto, array $breadcrumb, $page_title = NULL, array $tree = array(), $last_active = TRUE) {
+    $this->assertBreadcrumb($goto, $breadcrumb, $page_title, $tree, $last_active);
+  }
+}
diff --git modules/simpletest/tests/menu_test.module modules/simpletest/tests/menu_test.module
index 4c38502..82e17dc 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('administer site configuration'),
+  );
+  $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('administer site configuration'),
+  );
+
   // 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