Open furnace will only let you do one thing at a time.

I used to be able to open a furnace and change what was being smelted. Now if not everything is smelted, I need to take the unsmelted ore out, close the furnace, open the furnace, and add new item. Also happens when items are done smelting. Need to take smelted items out, close furnace, open furnace, put in new item.