I am really getting frustrated. I ruled out more or less everything. I have no UI connection to the battery in the UPS anymore but still the system goes either randomly to sleep (KDE, Unity, Gnome) or logs out and messes up the X server (XFCE).
The interesting thing is that I can distinguish between the log out screen of Unity/Gnome and XFCE. When running XFCE I all of a sudden see the logout screen of Unity/Gnome and not of XFCE. So something in the system of Gnome/KDE causes a log out or a sleep.
I am ready to go back to a simple window manager but still not sure if that really will help my problem.
Lets see what the next release of Ubuntu brings. At least it is not that long anymore…