I'm experiencing this problem nearly (but not quite) 100% of the time on an up-to-date (as of two-days ago) debian "unstable" system. This is with KDE 3.3 and in fact I didn't have the problem at all until the KDE 3.3 update.
Video driver is tdfx under xfree86-4.3 If you need more info, let me know. Thanks, Tony