This has been driving me nuts for years. I'll be clone stamping something, I'm on frame 45 and clone 829, and the while I'm painting, the stamp won't "release," meaning when I let go of the mouse, the stamp tool remains engaged and paint chaos begins. I have not found a way to reliably release the tool other than button mashing. Caps Lock doesn't work, saving doesn't work.
It is extremely frustrating and I'm surprised to find that no one has posted about it!