Today, I received a new version of xserver-xorg-video-intel (2:2.3.1-1) and everything is working again. From my point of view, this bug can be closed. Sorry again for filing this bug with inflated severity, I really felt it was correct, because of possible data-loss in all other running applications. Thanks for a fast solution. If I have to do anything to close the bug, just drop a note. Armin