Furnace is giving unlimited xp

There is a furnace that is connected via hoppers (Filling it up with material and then emptying it into a chest, and any time someone takes 1 thing out of it, its gives a lot of xp, no matter how many times you take one item. Usually this is normal after your smelt a lot of stuff, but to a certain extent. And the furnace is not stopping, and is giving infinite xp that people are managing to get from it.