On LG G2 running KitKat on T-Mobile...

I put 6 iron ore into a furnace with 2 coal for fuel.
Pulled up the Game Menu by clicking the phone's back button (it's a virtual button on the LG G2).
Selected Quit to Title.
Exited game by clicking the phone's back button.
Restarted the game and loaded the same world.
When I checked the furnace, it was empty when the iron ore and coal should have all been there.

It was not in my inventory and I checked around and see that everything else was up to date.