Unused Ore Vanishing When Retrieving Furnace

Added both iron ore and coal to furnace. Had ore left in furnace, when coal had run out. Used stone pick-axe to retrieve furnace, thinking that the unused ore would be returned, only to notice that the unused ore had vanished.
Tried to duplicate this and was successful in a duplication. Unused ore vanished, again.
All this was whilst I was on my realm and using the new City texture pack.