Pressure treated is one of the toughest to keep anything on. As one post has already said if the Treated maybe wasn't given enough time to weather, peeling would be pretty much expected. Also if the deck is very close to the ground moisture will wicked through and cause problems. For PT decks a tranluscent or semi trans stain are usually recommended....but even these can peel off if there is to much moisture in the wood. Not only that but the grain of yellow pine tends not absorb the finish in areas. All in all PT is tough with truly no guarantee of the net result of any finish.....