Terminal Server user cannot reconnect to 1st session

[humbletech99]

I have terminal servers running Windows Server 2003, and a rare fringe case seems to crop up about once a month for some random user in the company on some random terminal server.

The situation is that all users are allowed only 1 session on any terminal server, this is set by GPO. Occasionally however, a user connects and instead of getting reconnected to their one session, they get a second session. After this, they seem to get a new session every time and cannot reconnect to the first session.

The only thing I've managed to do on this is to reset every single session by such a user, losing unsaved work/long running processes, after which they get back to opening and using a new 1 session as normal which they can then reconnect to.

Windows eventlog hasn't turned up anything relevant.

Any ideas why this happens or how to fix it/prevent it from happening?