for regexp, we need 3 backslashes

Admin/Admin.php

@@ -52,7 +52,7 @@ abstract class Admin implements AdminInterface, DomainObjectInterface
     const CONTEXT_MENU       = 'menu';
     const CONTEXT_DASHBOARD  = 'dashboard';
 
-    const CLASS_REGEX        = '@([A-Za-z0-9]*)\\\(Bundle\\\)?([A-Za-z0-9]+)Bundle\\\(Entity|Document|Model|PHPCR|Phpcr|Doctrine\\Orm|Doctrine\\Phpcr|Doctrine\\MongoDB|Doctrine\\CouchDB)\\\(.*)@';
+    const CLASS_REGEX        = '@([A-Za-z0-9]*)\\\(Bundle\\\)?([A-Za-z0-9]+)Bundle\\\(Entity|Document|Model|PHPCR|Phpcr|Doctrine\\\Orm|Doctrine\\\Phpcr|Doctrine\\\MongoDB|Doctrine\\\CouchDB)\\\(.*)@';
 
     /**
      * The class name managed by the admin class