Infinite XP (experience) furnace exploit

The stored experience in a furnace can be collected repeatedly an unlimited number of times.

 

Steps to reproduce. 

1. Smelt items in a furnace. 
2. Attach a hopper and chest to collect the furnace output.
3. After a large amount of items have been smelted, lock the hopper with a lever. 
4. Allow the furnace to continue smelting items and collect them from the furnace one by one, without taking any items out of the chest.
5. Each time you collect another item from the furnace you get a massive XP amount. 

 

Expected behavior:

Total XP collected will be based on the number of items smelted.

 

Observed behavior:

Each single item taken from the furnace draws the amount of stored XP based on the chest contents. In other words, the stored XP amount is never reset as long as the hopper and chest still contain the smelted items, but instead the stored XP can be used many times. 

 

There is a YouTube tutorial on this glitch at https://youtu.be/dUtYdklQnhc