I may have found a workaround. I exited full-screen mode and noted that all three view modes became enabled. I then dragged the screen edge until I effectively had a full-screen image...all three views remained enabled and worked fine. I'd be interested to know if this works for anyone else. FYI, I'm using a MacBook Pro running Lion. Also, I've never used a Mac until yesterday so please pardon this post if it's a no-brainer.