super smelter with smoker gives copious amounts of exp

In a friends realm, we encountered a supposed bug that occurs with super smelters with smokers (it could be with all furnace variants, I have not tested if a blast furnace or regular furnace do the same thing). If you were to build a super smelter (one that looks like this: https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.instructables.com%2FFully-automatic-minecraft-furnace%2F&psig=AOvVaw3s8K2602hbWQlufvpjPtoO&ust=1622153486473000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCLiX-vSu6PACFQAAAAAdAAAAABAD ) with a smoker furnace, and remove the bottom hopper going from the smoker to the lowest chest and take out, say, a baked potato from smelting a raw potato, you would get a large amount of exp upon collecting the cooked item. This would last up until around the 20th/30th food item was smelted. I don't see why this would be a feature, so I am assuming this is a bug.