Second, if that doesn't work, you can try disabling atieventsd entirely(run sudo /usr/sbin/update-rc.d -f atieventsd remove or try an app like sysv-rc-conf), with the caveat that power and fan speed management will no longer function (the card will run with full power and fan speed at all times).
Third: Wait around for AMD to produce a driver that isn't quite so defective. Or for the radeonHD driver to progress a bit. If you find a solution, I implore you to please post it here (I have the same issue with my HD3650).
You might find some nuggets of wisdom in this thread or this thread, but perhaps not. My fingers are crossed for you.