I found this bug report https://bugs.freedesktop.org/show_bug.cgi?id=5792 Which says "As it turns out this problem is caused by the snapshot builds using outdated Xorg 6.9 sources that are incompatible with the current i915 driver from Mesa. i915 snapshots 20060123 and older should still be OK." So I guess the problem will go away with the next update of mesa.