'Change Chatroom' button text disappearing

I have no idea if this is just a problem with my computer, but after a while, the button 'disappears'. The blue part is still there, but the text appears like so: http://img3.imageshack.us/img3/5682/changechatun7.png

After hovering my mouse over it, it returns to normal.

It's not really a significant problem, I just thought I'd bring it to your attention.Score is 10