Comment 15 for bug 566788

/dev/shm is a tmpfs, and tmpfs in the kernel has a default mode of 01777. I don't see how this could be happening without a) an /etc/fstab entry overriding the /lib/init/fstab entry, or b) a rogue local script running at start-up that's changing the mode.

I certainly don't see any bugs in mountall here, and can't reproduce this - so if someone is still seeing this in 12.04, I'm afraid we're going to need more information to figure it out.