User <-> Group Assignment with LDAP

Hi,

I have configured my LDAP Connection in Userman and all Groups and Users are imported correctly.

But: No user is assigned to any group.

Queries performed by FreePBX (limited to one user and group currently) are

ldapsearch -w pass -H "ldap://ldap.organization.ac:389" -D "cn=admin,dc=ldap,dc=organization,dc=ac" -b "dc=ldap,dc=organization,dc=ac" -s sub "(&(objectclass=person)(cn=we91))" "cn=*" cn

# extended LDIF
#
# LDAPv3
# base <dc=ldap,dc=organization,dc=ac> with scope subtree
# filter: (&(objectclass=person)(cn=we91))
# requesting: cn=* cn 
#

# we91, ldap.organization.ac
dn: cn=we91,dc=ldap,dc=organization,dc=ac
cn: psuet

# search result
search: 2
result: 0 Success

and

ldapsearch -w pass -H "ldap://ldap.organization.ac:389" -D "cn=admin,dc=ldap,dc=organization,dc=ac" -b "dc=ldap,dc=organization,dc=ac" -s sub "(&(objectclass=groupofuniquenames)(cn=voip))"    

# extended LDIF
#
# LDAPv3
# base <dc=ldap,dc=organization,dc=ac> with scope subtree
# filter: (&(objectclass=groupofuniquenames)(cn=voip))
# requesting: ALL
#

# voip, ldap.organization.ac
dn: cn=voip,dc=ldap,dc=organization,dc=ac
cn: voip
description: VOIP Nutzer
ou: groups
ou: groups-netzwerk
objectClass: groupOfUniqueNames
objectClass: top
uniqueMember: cn=we91,dc=ldap,dc=organization,dc=ac

# search result
search: 2
result: 0 Success

My full configuration:

What am I doing wrong?!
I’m somewhat unsure about the selection of “Group Member Identitfier Attribute” but wouldn’t see alternative values that make more sense.