This isn't a WoW related problem. I have the same issue running LotRO. Usually IS closes when this happens to me, and just restarting it, seems to solve whatever problem I had.

On another note, IS is designed to load only the missing windows when you launch the character set a second, third, etc. time.

But there are other issues that just cropped up, after his latest patch. Hopefully, he'll let us revert (those of us having the troubles) or get a fix out soon.