Emacs+Keyboard lockup with metacity

I recently upgraded my machine to 8.10 (Intrepid Ibex) and it's been working mostly okay. I am using a Thinkpad T42.

I am using the free ATI drivers and they handle compiz pretty much out of the box. Unfortunately, my system occasionally gets completely locked up with compiz and because of this, I reverted back to metacity.

Things work fine until I use Emacs for anything. Some times (once out of every 20 times or so), when I switch focus from a maximised Emacs to another application (either a window cycle or a desktop switch), my keyboard just stops responding. My mouse moves around but can't click on anything. I can 'fix' this by switching to a virtual terminal C-A-F2 or something and switching back to X.

This problem is there with emacs-snapshot and with emacs22.

The only 'customisation' I've done which might cause this (as far as I can think) is that I edited the xkb files under /usr/share/X11/xkb/ to add a rule to map Super to my right Alt key and Alt/Meta to the left Alt key. I don't have a windows key on the laptop.

If there's any more information that might help, please let me know.

This thing is becoming a deal breaker and I'm seriously considering moving to another WM and ditching Gnome altogether although I've been with it for the better part of the last decade.