Cycles rendering at unwanted times

I just ran across a strange issue. While I’m working with my model, the program switches into the camera view and begins rendering the scene completely on its own, pulling me out of what I was doing. It seems to do it any time I try doing anything at all. Anyone know why and how I can stop it? Thanks.

You may be pressing a key combination that does this - likely F12 (on my installation), and also ALT X (but I may have put that one in).