Hmm, I don't know. about edit/undo. It's odd, really, because, if I do test scene and mess with with a bit and try to use the buttons, they react exactly as I've been told they should. However, whenever I've had a complex scene and rendering is mostly complete, the scene CHANGEs when I inadvertently hit one of the buttons; it doesn't save. If this comes up again, I'll try edit/undo. I have a feeling, though, that it won't do the trick, but you never know. Thanks for the thoughts, guys. Has no one else ever had this happen to them?