Furnace can't put item on furnace if they are on his side, on the top of the furnace it work but not on thé side, i also try with chest and it works when the hopper IS on the side (during thé vidéo with the chest test, i use m'y cobbleston generator and one of the cobbleston got burn in the lava, hé didn't disapear)

I didn't do a glitch or anything else for make the hopper not working, i discover it when i was trying some things.