[Dave at Pelican Parts]

The knob is reverse-threaded, but I thought the plastic part was much larger than a quarter. Is it indeed the manual opening knob?

The knob is twisted to open the light up or close it down. (Clockwise to do either.) If the light switch is "off", when the light gets open enough, the closing circuit will take over and cycle the light the rest of the way open and then close it. So the behavior you saw is normal and expected.

--DD