Turntable Question

I know this is sort of a "shot in the dark," but I figure I'd give it a try.

I got my dad's old turntable out today, and hooked it up to my stereo. The sound quality is great, and it seems to run smoothly, but for some reason, the turntable won't stop rotating after I press the "return" button. In fact, the turntable keeps rotating the entire time it's plugged in.

The manual says that the turntable should stop after the tonearm is back in the arm rest, so I'm sure that the table is not functioning correctly.

Does anyone know what to do in this situation?

The turntable is a Pioneer PL-115D, if that helps.