Samsung Galaxy S4 Phone
All of a stack of furnace items disappear from your furnace inventory if you move some (but not all) of that stack of it into an empty furnace and then try to move those items back into your inventory. If you do this with items in the burning chamber they disappear from your inventory permanently. If oyu do this with items in the smelting chamer they disappear from your furnace inventory but reappear in your inventory when you exit the furnace and look in your inventory.
Example of how to reproduce:
Get a stack of 4 wood and a furnace. Place 3 of the wood into either the lower slot (burning stuff to heat the furnace) or the upper slot (smelting into charcoal in this example). Now tap the stack of 3 wood in that chamber. I expected to see a stack of 4 wood backin in my furnace inventory, instead all 4 wood (the 1 in my inventory and the 3 in the furnace) have disappeared. When I exit the furnace the wood is still there in my inventory.