I just found an exploit to gain essentially infinite iron with the GraveStone mod installed. When any kind of grave from GraveStone is smelted in an alloy furnace, it gives back an iron block. This is an exploit because graves can be created with a stick, plank of wood, and an iron ingot, so essentially for the price of a stick, a plank, and furnace fuel, you can turn 1 iron ingot into 9, as many times as you want as long as you have the wood. Judging from the alloy furnace recipes, this may be due to BP automatically adding smelting recipes for items where it will give back some metal involved in the recipe, even when items have the same ID and different NBT or metadata or what have you.

It's possible to add these to a blacklist so that they are no longer recycled by the Alloy Furnace.