The problem vanished after I updated my "xserver-xorg*" Packages. Here is the output of aptitude -F "%p%V" search ~ixorg xorg 1:7.2-5 xorg-docs 1:1.4-2 xserver-xorg 1:7.3+2 xserver-xorg-core 2:1.4-2 xserver-xorg-input-kbd 1:1.2.2-3 xserver-xorg-input-mouse 1:1.2.2-5 xserver-xorg-video-intel 2:2.1.1-4 Regards, Martin