The lock pin itself is about 1/4 inch square. It moves up and down on a hinged (and lightly spring loaded) horseshoe shaped pivot bracket. If the adjustable latch on the door is pushed upward too far, you have to push the button on the dash to release the lock too far in. That causes the latch pin to flip out of its keeper on the underside of the dash.
You can actually worm your arm in up over the glovebox and grab that latch pin and direct it back inside the hole through the keeper and it will drop back down thru the hole. Then look at both you latch adjustment and the keeper adjustment. After those have been adjusted properly, the latch pin will never pop up under the dash again.
Lubriplate that square latch pin too.