Occassionally if I click an icon (usually on my desktop) it'll just "stick" to my mouse pointer, it'll appear as if I am still clicking and holding the icon, and it drags around. I also can't trash, drop or do anything with it. Other programs on the computer can't be used either because it's still using that icon. I'm forced to use keyboard commands to restart Finder... which works until I click any other icon again. What's going on?