Update to Drupal 8.1.2. For more information, see https://www.drupal.org/project/drupal/releases/8.1.2

core/lib/Drupal/Core/Theme/Registry.php

@@ -13,6 +13,13 @@ use Drupal\Core\Utility\ThemeRegistry;
 /**
  * Defines the theme registry service.
  *
+ * @internal
+ *
+ * Theme registry is expected to be used only internally since every
+ * hook_theme() implementation depends on the way this class is built. This
+ * class may get new features in minor releases so this class should be
+ * considered internal.
+ *
  * @todo Replace local $registry variables in methods with $this->registry.
  */
 class Registry implements DestructableInterface {
@@ -764,4 +771,5 @@ class Registry implements DestructableInterface {
   protected function getPath($module) {
     return drupal_get_path('module', $module);
   }
+
 }