I have to practice a little to be sure to automatically wrap my thumb over the grip after pushing the safety. Shooting clays with the safety on fire before starting does not do much to develop the right habit. A little practice switching the safety and wrapping the thumb seems to work. You could even take off the barrels and fore end and practice the move now and then during commercials, etc.
Anyway, you could test the gun, making sure your thumb is wrapped over the grip, to see if the safety stays put when you do it that way.
