Comment 9 for bug 108484

Marius:
Your issue is different. This sounds like X is being told to a virtual desktop size of 1024x768 but a "regular" size of 640x480. This often happens if you have a smaller mode before a larger one in your /etc/X11/xorg.conf . Whatever the cause, it is unrelated to this bug and I would recommend filing a new bug report and attaching your /etc/X11/xorg.conf file to it.