It doesn't matter whether the engine is accelerating or decelerating, the crank is still turning in the same direction. The crank is still driving the cam in the same direction, and the cam is still driving the oil pump in the same direction. The cam is being forced back towards the back of the block by the resistance of the oil pump drive.

1970 Road Runner 505 cid MCH CNC ported Stealth heads MP 528 camshaft 4 speed GV overdrive 11.98 @ 117 on street treads