Furnaces, smokers, and blast furnaces unloaded by hoppers give incorrect experience for smelted items

Furnaces and their variants (smokers and blast furnaces) which have been unloaded by hoppers give the incorrect amount of experience.

 

Expected behavior:

No matter how a player smelts and removes items from their smelting apparatus, the experience given should be consistent.

 

Observed behavior:

When smelting any material that gives experience, if items have been removed via a hopper, the player receives more experience than the items smelted.

 

How to reproduce:

1. Start with 0 XP (fresh death, creative /xp -1000L @s, whatever you want)
2. Place a furnace and smelt 10 gold ore without removing the resultant gold
3. Remove the gold all at once.
4. See that your XP has gone from 0 to 1 level and about 5.5 notches (not sure what the technical term for the little divider marks are) by smelting and collecting 10 gold ore.
5. Remove all of your XP (see step 1)
6. Place a hopper beneath the furnace.
7. Smelt 8 gold ore, letting the hopper remove the gold
8. Remove the hopper
9. Smelt 1 more (the 9th) gold ore and remove it
10. Smelt yet again 1 more (the 10th) gold ore and remove it.
11. See that your XP has gone from 0 to 2 levels and about 3 and a sliver notches by smelting and collecting 10 gold ore.
12. Remove all of your XP again (see step 1)
13. Smelt 10 more gold ore without removing it
14. Collect it all at once
15. See that your XP has gone from 0 to over 3 levels from smelting and collecting 10 gold ore.

 

This procedure should work with both the smoker and the blast furnace.  Obviously with the smoker you'll have to use meat and you'll get different XP benchmarks.