Hopper doesn't pull out items that were smelted in the furnace

The Hopper refuses to take out an ingot from the furnace that has been smelted. It only works when you place the hopper under the furnace after the ores have been smelted. So in order to take the ingots out, you have to place the hopper when it's done. The Hopper will not take it out during the smelting process.