When you are smelting a number of items in a furnace, once the last item in the furnace is being smelted, the progress bar will freeze and the item will not be outputted. This progress bar freeze occurs at about 50-60% completion, and the only way to get it to continue is to break the furnace - even then, you do not get even the raw item back - only the Furnace item and the fuel you were using.

It would be good to see this fixed, as it does mean a lot of resources are wasted.

Thank you,