I 've been using LR for a loooong time and never run into this. When I flag a photo (Command P) the frame advances to the next photo. I don't want this to happen. I'm sure I've hit something to cause this, but don't know how to reset it back to NOT moving to the next frame.
Turn off your caps lock. If the caps lock key is activated Lightroom also will auto advance. It is a feature that is there to help expedite rating images and other such tasks that you might want to get through quickly.
Thanks so much Jim. Exactly the answer I was looking for.