I had this happen to me a while ago, but it cleared up for me last week. I thought it was due to a patch or something but it could also be because I've been running the foundry in windowed mode to make spellchecking easier.
So if you're getting it now I guess it wasn't a patch and was the windowing thing. Try running the foundry in windowed mode (just via the little tab in the upper left when you mouse hover over the corner). Perhaps that will help.