When I add wood to the furnace on a LAN world I joined, it replenishes the fire without actually using up the wood. I can then take the wood out and use it again when the fire goes out for infinite fuel. This only happens for the first piece of wood you put in. If you put in a bunch and leave it, it will start using it up after the first piece is "used". But if I put in one piece, I can take it out and just put it back in when the fire dies, and repeat.

This only happens on the client in multiplayer. Attempting to do the same trick on the host device doesn't work, and does actually use up the wood.

Nokia Lumia 521 Windows Phone 8.1 host and Motorola Droid X2 Android 2.3.5 client, both running MCPE version 0.11.1.