I installed MGA6dev1 and updated to the latest updates (over 1149 updates today).
I note that if you add an application to the task/toolbar, the next time you login as a user, you re-enter the session to a black screen with only one application running.
If you do not add an application to the toolbar, you still login okay.
I've added bug https://bugs.mageia.org/show_bug.cgi?id=18644 but thought it best to list this problem here since this is also a blackscreen problem, but video still runs okay (mouse runs, 1 app still appears), while with topic viewtopic.php?f=15&t=11020 that appears to be a session where video fails at the X level.