I was in my skeleton farm to get to the level 33 for repair my diamond boots, when I got 32 level I closed my world to search how many skeletons I would kill to get 33 levels, I found it and reopen my world, and when I kill a skeleton I get to level 33 just like if I was with 0 exp and get 1 level. I try to repeat the process and I've got 34 levels.