Hoppers can be used a fuel in furnaces

Well, they come from chests, so that would make sense.

Can confirm, a hopper has the same effect as a chest when placed in the furnace fuel slot. Processes 1 1/2 items.

Not sure if intentional as it is made of a wooden chest in the recipe, however, it is clearly more of a stone item in appearance making this "feature" appear odd.

Yeah, I could understand both sides here.

Take note that a tool made from wooden sticks and stone, iron, gold or diamond do not burn in the furnace, only purely wooden tools can be used as fuel. So from the point of consistency with other items I voted for this as a bug. Similarly a storage minecart can't be used as a fuel.

However, oddly enough, a boat and a wooden door can't be used as fuel either - might want to reconsider those as well. Not that anyone would likely use those ingredients much anyway though, lol.

Confirmed!

Possibly related to MC-5991