After I found some iron,I smelt it in furnace.Then,I exit the game and clear my
app history and enter my world.It just left a burning furnace.And my iron DISAPPEAR!!!!!!!!

Step:
1.Put some items you want to cook in furnace
2.When it is cooking,exit the game and clear your app history.
3.Go back to your world
4.It just leave a burning furnace with no items inside