When I went mining on a Multiplayer world, I put 45 Coal and 9 Iron Ore into a Furnace. And I left the Furnace to get more Ore, but I waited until I could see the fire inside the Furnace. The fire never showed up and i waited 3 seconds after to see what would happed. So I re-entered the Furnace and I saw everything there for 2 seconds, then everything vanished into thin air?! Please help and respond to this. (:<
I get this bug too with 0.13.
Until they fix it, don't use shift-click to put stuff in Furnace - use click to pick up, move pointer to Furnace and click to put in. This works every time.