This happens to me all the time and it is so annoying. I use Spaces and quick look on files frequently. Sometimes I'll be looking at a file using Quick look (using the spacebar) and I'll switch spaces accidentally before closing the quick look. The quick look will stay open in the next space, but when I try and close it ,it will jump back to the previous space. If I try and use my magic mouse swipe it won't work. If I use the keyboard shortcut to move to another space it will work, but an empty quick look window pops up. If I try close it it will jump back to the previous space. It will keep doing this until I do some kind of combination of closing and quick look and it will eventually clear the problem. Anyone else have this problem? It happens on 2 different Macs I have.