Comment 4 for bug 571944

Specifically, this happens when you drag a Nautilus desktop icon quickly. Start the drag prior to the icon becoming selected.

To reproduce: In a quick, continuous, motion, move the mouse cursor to a desktop folder, left click and drag. Sometimes, the folder does not move. When this happens, the mouse is left in the drag state and you can not click on anything nor alt-tab through windows. Only killing Nautilus will free your mouse.