Comment 2 for bug 281971

Indeed that's actually the same problem as in bug 270342. Since there can't really sanely two guest sessions at the same time, it would be nice if the "Guest sesssion" entry could only appear if there isn't a session running already.

If it helps, I can add a helper script like "/usr/share/gdm/guest-session/session-running" or so. Or you just check if user "guest" has a session running.