Comment 8 for bug 200805

Update:

Adding a Display subsection to the Screen section of my xorg.conf, specifying a Virtual size
equal to the size of the external problem has solved the issue for me.

Section "Screen"
        Identifier "Default Screen"
        Monitor "Configured Monitor"
        Device "Configured Video Device"
        SubSection "Display"
            Virtual 1280 1024
        EndSubSection
EndSection