--- a/services/univention-ad-connector/modules/univention/connector/__init__.py	
+++ a/services/univention-ad-connector/modules/univention/connector/__init__.py	
@@ -1423,7 +1423,7 @@ class ucs:
 					retlist.append(l.lower())
 				return retlist
 			else:
-				return elements
+				return elements.lower()
 
 		def dict_lower(dict):
 			if isinstance(dict, type({})):