--- __init__.py	2020-08-05 12:46:10.260000000 +0200
+++ /usr/lib/python2.7/dist-packages/univention/connector/ad/__init__.py	2020-08-05 13:12:40.060000000 +0200
@@ -363,7 +363,8 @@ def samaccountname_dn_mapping(connector,
 
 				else:
 					newdn_rdn = [('cn', fst_rdn_value, ldap.AVA_STRING)]
-					newdn = ldap.dn.dn2str([newdn_rdn] + exploded_dn[1:])  # new object, don't need to change
+					default_dn = connector.property[propertyname].con_default_dn
+					newdn = ldap.dn.dn2str([newdn_rdn] + ldap.dn.str2dn(default_dn))  # new object, don't need to change
 
 				ud.debug(ud.LDAP, ud.INFO, "samaccount_dn_mapping: newdn: %s" % newdn)
 			else:
@@ -415,7 +416,8 @@ def samaccountname_dn_mapping(connector,
 						newdn_rdn = [(dn_attr, dn_attr_val, ldap.AVA_STRING)]  # guess the old dn
 					else:
 						newdn_rdn = [(ucsattrib, samaccountname, ldap.AVA_STRING)]  # guess the old dn
-					newdn = ldap.dn.dn2str([newdn_rdn] + exploded_dn[1:])
+					default_dn = connector.property[propertyname].ucs_default_dn
+					newdn = ldap.dn.dn2str([newdn_rdn] + ldap.dn.str2dn(default_dn))
 			try:
 				ud.debug(ud.LDAP, ud.INFO, "samaccount_dn_mapping: newdn for key %s:" % dn_key)
 				ud.debug(ud.LDAP, ud.INFO, "samaccount_dn_mapping: olddn: %s" % dn)