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...then just setup a regular check to see if the user/session is still there, if not, return the entry to its default.
I just wanted to prevent potential security problems. If a single user can log in, then someone else, potentially, could log in with the same account and mess things around.
That's not true, you can't state that as concrete. There is always someone out there who will do that, shared PC's or public terminals for starters.