Aerobatic props tend to be set up to revert to coarse pitch if oil pressure is lost, because flinging the aircraft around the place can often lead to temporary fluctuations in pressure, and you don't want the potential for frequent engine overspeeds. A classic symptom of "sticky balls" in the inverted oil system is having the prop start to wind back in a vertical up-line (the ball valve is often mounted at a slight angle, so that assuming you do hit a perfect vertical line the system is still working fully in one orientation).