When Easy Magic is installed, the enchanting table doesn't take into account any modded bookshelves placed around it for calculating maximum possible enchantment level, only vanilla bookshelves are taken into account.

The unmodded enchanting table correctly takes modded bookshelves into account.

Confirmed with bookshelves from the following mods:

Better End: https://www.curseforge.com/minecraft/mc-mods/betterend
Charm: https://www.curseforge.com/minecraft/mc-mods/charm

Fixed by #8 .