The bug
You cannot shift click smeltable items in a furnace
Example
Try to shift click cobblestone in a furnace
→ ❌ The cobblestone doesn't end up in the smelting slot
Linked issues
is duplicated by 18
13 more links
You cannot shift click smeltable items in a furnace
Try to shift click cobblestone in a furnace
→ ❌ The cobblestone doesn't end up in the smelting slot
Confirmed
furnace
Minecraft 18w06a, Minecraft 18w07a, Minecraft 18w07b, Minecraft 18w07c, Minecraft 18w08a, ..., Minecraft 18w11a, Minecraft 18w14a, Minecraft 18w14b, Minecraft 18w15a, Minecraft 18w16a
Minecraft 18w19a
Retrieved
Also, after placing smeltables into the furnace, shift+click fuel (i.e. coal) only visually places it in the fuel slot. The furnace does not start, and once you exit the furnace GUI the fuel is back in your inventory.
Note that shift+click fuel works properly if the furnace input is empty.