I suspect that it has something todo with the kernel-parameter hpet=force. I tried the current git-kernel (2.6.29-git3) with hpet=force and it worked and atm I have linux-image-2.6.26-1-686 without hpet=force and it seems to work, too. I'm going to try vanilla-2.6.26.8, today too, to see if this bug is introduced by the debian patchesor by the kernel.