I'd look at those group entries.
It seems to look OK ... here is the LDIF for the admin group
# Entry 1: cn=admin,ou=groups,dc=mydomain,dc=net dn: cn=admin,ou=groups,dc=mydomain,dc=net cn: admin gidNumber: 101 objectClass: top objectClass: posixGroup memberUid: mjuszczak memberUid: min