I have an issue with the terminal window on the Mac. Often when I am trying to copy text from the terminal onto the clipboard, I end up grabbing it accidentally for a drag and drop maneuver. This has been really annoying since I then had to drag it over to the trash can and try again. I found out there is an easier way to cancel this operation, and it applies to any drag and drop operation on the Mac. While dragging, press the Esc key on the keyboard. When you do this, you'll see the thing you are dragging goes back to it's original position. You can then safely release the mouse button and things will be back to their original state.