Same problem!!!
When I add a toolbar (even the quicklaunch) the same thing happens; it goes away after i restart. I thought it was a 3rd party software conflict. This is a stretch but do you have goback, norton antivirus, or programs called cjb netter or ioupus ac plug? It's probably a windows bug caused by something else that I can't put my finger on either. Also, it only occurs on accounts which I added after the XP installation.