I seem to have activated or triggered some setting (or stumbled upon a bug)that prevents me from un-clicking in the viewport. If I'm trying to rotate, pan, zoom or effect transforms on an object it simply will not let go. So I alt-click to rotate, when I release the mouse button it should stop rotating, but it does not. The only way to escape the rotate tool is to hit ESC which cancels my move.
I'm having the same problem. Were you able to figure it out? I just downloaded the trial of R16 and the program did it right from the start. The only way I can get it to let go is if I hit the ESC key and then it completely resets the object.