The bug
MC-124909 was fixed, however if you relog before removing the output item, no recipe is awarded
How to reproduce
Obtain iron ore
Remove the smelt iron recipe from yourself (
/recipe take @p iron_ingot
)Smelt the iron ore in a furnace
If you remove the iron now, you will get the recipe/experience as expected
Relog first
Remove the iron; no recipe or experience are awarded
Armchair analysis is that the "recipe used for smelting" is saved to the furnace block entity somewhere in memory but isn't serialized to NBT, so it's lost when the furnace is unloaded.
This is back with 19w07a.