Mission Control bug on Mountain Lion: Dragging Windows to Desktops Fails Regularly When I activate Mission Control and try to drag drag, say, two windows to another desktop, the first drag works fine. I can drag the window to the other desktop's thumbnail, which darkens, and then release the mouse, and the window moves to that desktop just as it should.

When I try to drag the second window, however, the recipient space won't darken—it doesn't register that I'm dragging the window over it—and when I release the mouse button, the window will snap back to its original position as though I'd dragged it to some other part of the screen.

When I initiate another drag on the second window (the third drag total) it'll work properly. Then, I'll drag another window and it won't work. It occurs every other time I drag a window, with perfect regularity, as far as I can tell.

Other points:


Non-working drags doesn't have to be over a space for the next drag to work. I could drag a window an inch, release it, and then pick it up and drag it to another desktop just fine.
The "new desktop" button never seems to suffer from this problem.
The problem also occurs on the guest account.


Any ideas how to fix it, or why it's happening? Any help is appreciated.
This has been killing me, too. But I went into the MC preferences pane and unchecked "Group windows by application." It worked.