Default groups/services for LDAP customers

[Mothra]

I've just recently set up a new OTRS system after a long break from OTRS, so I'm a bit rusty...

I've got a bunch of potential customers in Active Directory, and I've configured OTRS to have them authenticate successfully. The problem I have at present is that the settings for default groups and default services have no effect on these customer users. Is this expected behaviour, or have I missed something in my setup (I can post that here if necessary)?