Known, some problem in the /dev/mem logic. As only X.org 1.4 still uses this interface, I tend to ignore it until someone provides a patch. Newer versions uses the /sys/bus/pci/devices/*/resource* interface, can you please check if at least this works?
I can confirm this bug in stable: Lenny Package: xen-linux-system-2.6.26-1-xen-amd64 Version: 2.6.26-13lenny2 Package: xorg Version: 1:7.3+18 Test system is HP6715B.You mention using a newer version of Xorg. Lenny has 1.7. Is there a work round...?
Berni