Hopper can't put item in the furnace if they are on his side

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.