diff --git a/core/lib/Drupal/Core/Extension/ThemeHandler.php b/core/lib/Drupal/Core/Extension/ThemeHandler.php
index 1f366aa..b47fea1 100644
--- a/core/lib/Drupal/Core/Extension/ThemeHandler.php
+++ b/core/lib/Drupal/Core/Extension/ThemeHandler.php
@@ -196,6 +196,10 @@ public function enable(array $theme_list, $enable_dependencies = TRUE) {
       arsort($theme_list);
       $theme_list = array_keys($theme_list);
     }
+    else {
+      $installed_themes = $extension_config->get('theme') ?: array();
+      $installed_themes += $extension_config->get('disabled.theme') ?: array();
+    }
 
     $themes_enabled = array();
     foreach ($theme_list as $key) {
@@ -219,31 +223,38 @@ public function enable(array $theme_list, $enable_dependencies = TRUE) {
         ->clear("disabled.theme.$key")
         ->save();
 
-      // Update the current theme data accordingly.
+      // Add the theme to the current list.
       // @todo Remove all code that relies on $status property.
       $theme_data[$key]->status = 1;
+      $this->addTheme($theme_data[$key]);
+
+      // Update the current theme data accordingly.
       $current_theme_data = $this->state->get('system.theme.data', array());
       $current_theme_data[$key] = $theme_data[$key];
       $this->state->set('system.theme.data', $current_theme_data);
 
+      // Reset theme settings.
       $theme_settings = &drupal_static('theme_get_setting');
       unset($theme_settings[$key]);
 
-      // Refresh the theme list as installation of default configuration needs
-      // an updated list to work.
-      $this->reset();
-
-      // The default config installation storage only knows about the currently
-      // enabled list of themes, so it has to be reset in order to pick up the
-      // default config of the newly installed theme. However, do not reset the
-      // source storage when synchronizing configuration, since that would
-      // needlessly trigger a reload of the whole configuration to be imported.
-      if (!$this->configInstaller->isSyncing()) {
-        $this->configInstaller->resetSourceStorage();
-      }
+      // @todo Remove system_list().
+      $this->systemListReset();
+
+      // Only install default configuration if this theme has not been installed
+      // already.
+      if (!isset($installed_themes[$key])) {
+        // The default config installation storage only knows about the currently
+        // enabled list of themes, so it has to be reset in order to pick up the
+        // default config of the newly installed theme. However, do not reset the
+        // source storage when synchronizing configuration, since that would
+        // needlessly trigger a reload of the whole configuration to be imported.
+        if (!$this->configInstaller->isSyncing()) {
+          $this->configInstaller->resetSourceStorage();
+        }
 
-      // Install default configuration of the theme.
-      $this->configInstaller->installDefaultConfig('theme', $key);
+        // Install default configuration of the theme.
+        $this->configInstaller->installDefaultConfig('theme', $key);
+      }
 
       $themes_enabled[] = $key;
 
@@ -251,8 +262,8 @@ public function enable(array $theme_list, $enable_dependencies = TRUE) {
       watchdog('system', '%theme theme enabled.', array('%theme' => $key), WATCHDOG_INFO);
     }
 
-    $this->resetSystem();
     $this->clearCssCache();
+    $this->resetSystem();
 
     // Invoke hook_themes_enabled() after the themes have been enabled.
     $this->moduleHandler->invokeAll('themes_enabled', array($themes_enabled));
@@ -284,15 +295,22 @@ public function disable(array $theme_list) {
         ->clear("theme.$key")
         ->set("disabled.theme.$key", 0);
 
+      // Remove the theme from the current list.
+      unset($this->list[$key]);
+
+      // Update the current theme data accordingly.
       unset($current_theme_data[$key]);
 
+      // Reset theme settings.
       $theme_settings = &drupal_static('theme_get_setting');
       unset($theme_settings[$key]);
+
+      // @todo Remove system_list().
+      $this->systemListReset();
     }
     $extension_config->save();
     $this->state->set('system.theme.data', $current_theme_data);
 
-    $this->reset();
     $this->resetSystem();
 
     // Invoke hook_themes_disabled after the themes have been disabled.
diff --git a/core/modules/system/lib/Drupal/system/Tests/Extension/ThemeHandlerTest.php b/core/modules/system/lib/Drupal/system/Tests/Extension/ThemeHandlerTest.php
index 0268f7d..95fdee9 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Extension/ThemeHandlerTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Extension/ThemeHandlerTest.php
@@ -73,7 +73,7 @@ function testEnable() {
     $this->themeHandler()->enable(array($name));
 
     $this->assertIdentical($this->extensionConfig()->get("theme.$name"), 0);
-    $this->assertFalse($this->extensionConfig()->get("disabled.theme.$name"));
+    $this->assertNull($this->extensionConfig()->get("disabled.theme.$name"));
 
     $themes = $this->themeHandler()->listInfo();
     $this->assertTrue(isset($themes[$name]));
@@ -141,14 +141,40 @@ function testDisable() {
 
   /**
    * Tests disabling and enabling a theme.
+   *
+   * Verifies that
+   * - themes can be re-enabled
+   * - default configuration is not re-imported upon re-enabling an already
+   *   installed theme.
    */
   function testDisableEnable() {
     $name = 'test_basetheme';
-    $this->testDisable();
-    $this->config("$name.settings")->set('keep', 'me')->save();
 
-    $this->testEnable();
-    $this->assertIdentical($this->config("$name.settings")->get('keep'), 'me');
+    $this->themeHandler()->enable(array($name));
+    $this->themeHandler()->disable(array($name));
+
+    $this->assertIdentical($this->config("$name.settings")->get('base'), 'only');
+    $this->assertIdentical($this->config('system.date_format.fancy')->get('label'), 'Fancy date');
+
+    // Default configuration never overwrites custom configuration, so just
+    // changing values in existing configuration will cause ConfigInstaller to
+    // simply skip those files. To ensure that no default configuration is
+    // re-imported, the custom configuration has to be deleted.
+    $this->configStorage()->delete("$name.settings");
+    $this->configStorage()->delete('system.date_format.fancy');
+    // Reflect direct storage operations in ConfigFactory.
+    $this->container->get('config.factory')->reset();
+
+    $this->themeHandler()->enable(array($name));
+
+    $themes = $this->themeHandler()->listInfo();
+    $this->assertTrue(isset($themes[$name]));
+    $this->assertEqual($themes[$name]->getName(), $name);
+
+    $this->assertEqual(array_keys(system_list('theme')), array_keys($themes));
+
+    $this->assertFalse($this->config("$name.settings")->get());
+    $this->assertNull($this->config('system.date_format.fancy')->get('label'));
   }
 
   /**
@@ -289,10 +315,22 @@ protected function extensionConfig() {
   /**
    * Returns a given config object.
    *
+   * @param string $name
+   *   The name of the config object to load.
+   *
    * @return \Drupal\Core\Config\Config
    */
   protected function config($name) {
     return $this->container->get('config.factory')->get($name);
   }
 
+  /**
+   * Returns the active configuration storage.
+   *
+   * @return \Drupal\Core\Config\ConfigStorageInterface
+   */
+  protected function configStorage() {
+    return $this->container->get('config.storage');
+  }
+
 }
diff --git a/core/modules/system/tests/themes/test_basetheme/config/schema/test_basetheme.schema.yml b/core/modules/system/tests/themes/test_basetheme/config/schema/test_basetheme.schema.yml
new file mode 100644
index 0000000..9cfe9ec
--- /dev/null
+++ b/core/modules/system/tests/themes/test_basetheme/config/schema/test_basetheme.schema.yml
@@ -0,0 +1,10 @@
+test_basetheme.settings:
+  type: system.theme.global
+  label: 'Test base theme settings'
+  mapping:
+    base:
+      type: string
+      label: 'Base theme setting'
+    override:
+      type: string
+      label: 'Whether the setting has been overridden'
diff --git a/core/modules/system/tests/themes/test_basetheme/config/system.date_format.fancy.yml b/core/modules/system/tests/themes/test_basetheme/config/system.date_format.fancy.yml
new file mode 100644
index 0000000..12ae886
--- /dev/null
+++ b/core/modules/system/tests/themes/test_basetheme/config/system.date_format.fancy.yml
@@ -0,0 +1,11 @@
+# Themes are not supposed to provide/install this kind of config normally.
+# This exists for testing purposes only.
+# @see \Drupal\system\Tests\Extension\ThemeHandlerTest
+id: fancy
+label: 'Fancy date'
+status: true
+langcode: en
+locked: false
+pattern:
+  php: 'U'
+  intl: 'EEEE, LLLL d, yyyy - kk:mm'
diff --git a/core/modules/system/tests/themes/test_subtheme/config/schema/test_subtheme.schema.yml b/core/modules/system/tests/themes/test_subtheme/config/schema/test_subtheme.schema.yml
new file mode 100644
index 0000000..034734b
--- /dev/null
+++ b/core/modules/system/tests/themes/test_subtheme/config/schema/test_subtheme.schema.yml
@@ -0,0 +1,7 @@
+test_subtheme.settings:
+  type: theme_settings_default
+  label: 'Test sub theme settings'
+  mapping:
+    override:
+      type: string
+      label: 'Whether the setting has been overridden'