Schema violation with LDAP and Groups/Roles

Trying to add groups (or roles) on a clean openldap directory I obtain the following error:

18:00:42,095 ERROR crowd.console.action.group.AddGroup: Operation failed; nested exception is javax.naming.directory.SchemaViolationException: [LDAP: error code 65 - object class 'groupOfUniqueNames' requires attribute 'uniqueMember']; remaining name 'cn=Test,ou=Groups,dc=XXXX,dc=XXX'

It seems Crowd tries to add the group entry without using the attribute uniquemember.

Same thing happens for Roles, while the creation of principals works fine.