Furnace fuel residue

I think it would be really helpful and logical if only the flammable stuff like wood, coal, blaze rods, etc., got burnt, but what can't be used as fuel will remain in the fuel slot

Example: Using a jukebox (8 wood and 1 diamond in the middle), will only leave behind the diamond, while the wood is burnt.

If the player is not the one putting the fuel directly into the furnace, the residue will go into a hopper if it's connected to it, or if not it will stay in the fuel slot.