The cause? Well, Toolfish loads on start up, as does ICQ... and it does this, and I can't get rid of it. Minimizing-maximizing doesn't clear it, dragging it off the screen and back on doesn't as well... and so on. Maybe it could refresh the buttons and such coming back from being minimized or something...

*By minimized, I mean put on the toolbar, but minimizing is easier to say.