Enchant Bug

What I expected to happen was...:
I enchanted my diamond sword with lvl 30. It should have taken my lvl 30 enchant.

What actually happened was...:
It only removed 3 levels.

Steps to Reproduce:
1. Place a level 30 enchant table
2. Give yourself level 30
3. Enchant level 30 on any item.
4. Then you'll see that it only takes 3 levels away.