The original issue works for me now on 13.2. I don't remember why I wanted to start two sessions, perhaps to debug some problems with the session. In any case, a user who runs into it would regard it as a bug if the session crashes without any explanation; I agree that this is not how things should behave in Linux. Session stuff should, imho, be primarily tied to the X instance, not to the user. In any case, the problem may be resolved by now.