When I insert a coal block (could be done with any smelting item i think) and enter the nether (the coal block already used, about halfway done), when I come back the furnace will start fully burning the coal again without the need of another coal block (it restarted the timer for the coal block i think). I don't know if this was in previous versions too, and it's not a game changer, but I just thought I'dd report it.