SBS 2003 RDP console session will not logout

We have an old SBS 2003 server on our test network which gets hacked about and rebuilt as needed.  After this latest rebuild it has started doing something a bit odd.

We can start an RDP console session and login as a user in the Domain Admins group fine and logout again. If we start an RDP console session and login as Administrator we can't logout of the session. The Logoff is logged in the Security event log but no logout occurs. The session remains open and active.

Has anyone seen this behaviour before and know a fix please?

Thanks

George