1) Added support for ShopKeeper npc's IllegalStack should ignore the shopkeeper NPC's and no longer flag parts of their GUI as invalid.
2) Added protection against the Piston/Observer/Armor Stand lag machine, this design uses a ton of pistons and armor stands to lag the server, the fix simply prevents pistons from pushing armor stands upwards. There should be no real reason to ever need to push an armor stand straight up and let it fall back down.