Never had THIS happen before!

May 12, 2019
Borrowed my dad's 2004, 4.6 Expedition to tow a trailer to move my daughter to college. I washed and waxed it and parked it. I set the parking brake, placed in PARK and when I went to turn the ignition switch OFF THE STARTER STARTED SPINNING WITHOUT ENGAGING THE FLYWHEEL! Now the engine shut down but the starter was spinning non-stop. I switched it back to the start position and it cranked right up and ran fine, the starter not spinning as long as the engine was running. Tried it again and same thing, engine stopped and starter was spinning wide open not engaging the flywheel. Anyone ever heard of or experienced this?