On Windows, resize the game window so it has plenty desktop visible on all sides. Now left click and rotate the protein and take the mouse right out of the window while the button is clicked... now move around to another side of the window and bring the mouse back in to the game... WHOA!

Basically, when mouse leaves the windows, the rotate operation needs to stop as though the mouse button was released.

http://fold.it/portal/node/37778