I have been having a problem getting a good photo exposure after recording video. I began the session shooting stills on P mode (ISO 1600), then switched to video, which exposed well. Trying to switch back to stills, I get a long shutter speed and crazy overexposure, and cannot manually change any settings to get a good exposure. Sometimes turning the camera off and on again helps. Sometimes not. It seems to be worse after a session of heavy use. What's happening?