diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 0794b3d..2caf6da 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1070,7 +1070,7 @@ function theme($hook, $variables = array()) {
     // array.
     foreach (array('preprocess functions', 'process functions') as $processor) {
       if (isset($base_hook_info[$processor])) {
-        $info = array_merge($info, array($processor => $base_hook_info[$processor]));
+        $info[$processor] = $base_hook_info[$processor];
       }
     }
   }
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockPreprocessUnitTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockPreprocessUnitTest.php
new file mode 100644
index 0000000..ddbc40c
--- /dev/null
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockPreprocessUnitTest.php
@@ -0,0 +1,56 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\block\Tests\BlockPreprocessUnitTest.
+ */
+
+namespace Drupal\block\Tests;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Unit tests for template_preprocess_block().
+ */
+class BlockPreprocessUnitTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('block');
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Block preprocess',
+      'description' => 'Test the template_preprocess_block() function.',
+      'group' => 'Block',
+    );
+  }
+
+  /**
+   * Tests block classes with template_preprocess_block().
+   */
+  function testBlockClasses() {
+    // Define a block with a derivative to be preprocessed, which includes both
+    // an underscore (not transformed) and a hyphen (transformed to underscore),
+    // and generates possibilities for each level of derivative.
+    // @todo Clarify this comment.
+    $block = entity_create('block', array(
+      'plugin' => 'system_menu_block:menu-admin',
+      'region' => 'footer',
+      'id' => config('system.theme')->get('default') . '.machinename',
+    ));
+
+    $variables = array();
+    $variables['elements']['#block'] = $block;
+    $variables['elements']['#configuration'] = $block->getPlugin()->getConfig();
+    $variables['elements']['#plugin_id'] = $block->get('plugin');
+    $variables['elements']['content'] = array();
+    $variables['content_attributes']['class'][] = 'test-class';
+    template_preprocess_block($variables);
+    $this->assertEqual($variables['content_attributes']['class'], array('test-class', 'content'), 'Default .content class added to block content_attributes');
+  }
+
+}
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 39e685e..767b499 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1038,7 +1038,15 @@ function system_theme_suggestions_page_alter(array &$suggestions, array $variabl
 function system_theme_suggestions_maintenance_page_alter(array &$suggestions, array $variables) {
   // Dead databases will show error messages so supplying this template will
   // allow themers to override the page and the content completely.
-  if (defined('MAINTENANCE_MODE')) {
+  $offline = defined('MAINTENANCE_MODE');
+  try {
+    drupal_is_front_page();
+  }
+  catch (Exception $e) {
+    // The database is not yet available.
+    $offline = TRUE;
+  }
+  if ($offline) {
     $suggestions[] = 'maintenance_page__offline';
   }
 }