I installed a kernel with the patch referred to in
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=526169#41 and the tiling
persists. However I managed to solve the problem by setting the Tiling
option to false as mentioned in
https://bugs.freedesktop.org/show_bug.cgi?id=21246#c10
Currently my /etc/X11/xorg.conf reads
Section "Device"
Identifier "Intel Corporation 82852/855GM"
Driver "intel"
Option "Tiling" "false"
EndSection
And I'm using a Thinkpad R50e.