Using current Linux kernel (ArchLinux, both stock and PF), X segfaults when flipping the screen around and closing (tablet mode). Killing and/or removing acpid fixes the problem, so I believe it has to do with the 'tablet-mode' acpi event. Someone else seems to be having this problem, but both of our first thought was to submit a bug report to X.org
Here is my Xorg.0.log:
This doesn't occur on Linux LTS. If I was smart, I would've noticed right away after uprading the kernel what version number but I'm still learning.