Furnace not working when fuel is taken out

when smelting items in the oven u can't take out it's fuel source, the oven will stop smelting after finishing the object you were smelting when taking the fuel out, but continue to  consume the fuelreserve it's running on.

Furnace will continue working if you put its fuelsource back in (an empty bucket will work too), this will not consume the fuel till it's reserve is empty