Not the default X Screen
No, its not the default X-Screen (black&white stippled pattern). It is on the first screen - but not on the second. On the second screen one can see vertical black&white stripes.
I did not intend to start a second Windows Manager as I don't need one on the second display - it's just for displaying video (with mplayer) - but I don't get this far.
To me it really seems that there is a driver bug - maybe there is a workaround?