Mint 14 won't shut down

[Quasimodo]

I installed Mint 14 (AMD64 Cinnamon) on a spare partition on my desktop system (I like to be able to go back to the previous version, so I always set up a new version to dual boot with the previous one): Tyan Thunder motherboard, dual Opteron 2 GHz CPUs, 8GB RAM, 150GB main HDD, 5 x 320GB HDD in a RAID5 array for bulk storage.

After installation, I rebooted and collected the usual shed-load of updates, including kernel version 3.5.0-22. After adding various extra packages I tried to restart, but the system hung after telling me thatit was about to shut down, and the Caps Lock & Scroll Lock LEDs on the keyboard flashed. The only way to get out of this was a hard reset. I've tried earlier versions of the kernel: 3.5.0-21, 3.5.0-19. 3.5.0-18 and 3.5.0-17. All give the same effect. I've also tried shutting down from the login screen and from a terminal (sudo shutdown -h now), with the same result. I can tweak GRUB so that the default boot is to Mint 13, which behaves properly; however I'd be grateful for any indication of whether this is a known bug or something peculiar to my setup.

I can, of course, provide any more detailed diagnostic information if needed.

Thanks in advance

Ian