Like nhusa said, in the hand cranked Model T world, this is what's known as a "free start". I too get one about half the time. Much more common in the T due to the ******** ignition coils, where the coils fire multiple times during a few degrees of rotation for each cylinder. Never had it happen to me in the As. Interestingly, before shutting off the ignition in any of his cars up until he passed in 1980, my father used to blip the gas pedal, and while the engine was still racing, he'd turn off the ignition. This was a carryover habit from the old hand cranked days, where you tried to get a charge of unburned gas in the cylinders when shutting down in order to make re-starting it that much easier.