Any xp that was gained by smelting iron or gold is now lost if a hopper is added to the bottom block of the furnace. Suggest adding a single drop, non-mineable ore item, ( chunk of iron/gold ore ) similar to coal, emeralds, red stone, etc + xp while mining iron and gold and allow this dropped item to be smelted without any xp gained from the smelting itself. This would allow xp to be gained by iron/gold mining without exploits.