The burnout issue happens when, in first gear (where the sprag or overrunning clutch holds the rear drum) the wheels suddenly grab......like burning out in the water box and letting the car roll out to the dry sticky pavement where the tires grab. This shocks the sprag clutch hard enough to damage it, tearing the outer race loose. Most manual valve bodies also apply the rear band in first to help prevent this. This is why a bolt in sprag (much stronger) is a must in a performance build.
A damaged sprag will allow the forward drum to spin up to two or three times engine rpm on your next hard launch or burnout in first. The stock forward drum explodes like a grenade somewhere around eight or ten thousand rpm.