Unlimited experience from the furnace

When I cook materials in the furnace I have the opportunity to have infinite experience.

An example to explain me better.
1) I use the furnace with Hopper above and below the furnace to cook 20 stone stacks.
2) lock the lower hopper with a lever
3) I collect 1 item from the furnace and take 10 levels of experience
4) I collect another item to be cooked and take 5 more levels
5) I collect a third item and take 5 more levels etc..
6) infinite loop

in 10 minutes i reached 100 experience levels starting from 0