Bane of Arthropods 5 from 15 bookshelf enchantment table

Enchantment table gave me Bane of Arthropods 5, although that is impossible.

 

Steps to reproduce

1. Get a 15 bookshelf enchantment setup
2. Take a diamond sword and enchant it, then send it into a grindstone, until you get Bane of Arthropods 5