I have this happen quite often actually and the way to fix this is to mouse over a different folder or file in your file tree in the editor. I always had to close it too before I realized that. Been gonna report this one too but I didn't know if it was the editor or just me. Guess I know now lol.
I can't replicate it either which makes it hard to track down. It's such a random thing that it makes it hard to reproduce it to figure out what's causing it.
All I know is once in a while (about every 2nd or 3rd time I run the editor) when I mouse over something in my file tree, that is what happens, the tooltip just stays there.
Windows 7 Ultimate 32 bit
Nvida GeForce GTX 560 Ti
4 Gig Ram