I am not a mechanic by trade, though I do a lot of work on my own cars out of sheer necessity (no money...lol), but if my car did what you described and I was not mechanically inclined, I would take the car to a shop immediately. If you are mechanically inclined, inspect the brake fluid, vacuum line to the brake master cylinder or booster, the pedal itself and all of the mechanical linkage from the pedal to the master cylinder. I would thoroughly go over the entire system. I have never had that problem and it is puzzling to me. Perhaps one of the AF enthusiast will pick up on this thread and reply with more specific info. Sorry so vague.