Anvils will not reject an enchanted book even if the resulting item is the same as the original one

The bug

Anvils will not reject a enchanted book if an item has the same enchantment but on a higher level.

How to reproduce

1. Go into creative mode and get a diamond axe, an efficiency 5 book, and a efficiency 3 book
2. Add the efficiency 5 book to the axe
3. Give yourself at least 30 levels of xp
4. Go into survival mode
5. Add the efficiency 3 book to the axe
   → Notice how the anvil doesn't reject it