When this happens to me (mostly as superuser, not much as normal user) I have to reboot. Very irritating but for me it fixes it. Wish I knew how to rezero it again from the CLI.
Try rebooting or logging off and on. Should fix it.
It happens in Konqueror too for me. Has been going on for three releases that I can recall, but 99% of the occurrences for me are as root user (superuser).