According to the new guidelines enchanted books should have the Rare rarity:

When an item is enchanted, their rarity status is now increased depending on their base rarity

• If the base rarity of an item is Common or Uncommon, it will become Rare when enchanted
• If the base rarity of an item is Rare, it will become Epic when enchanted
• If the base rarity of an item is Epic, it will stay Epic when enchanted

However, they have the Uncommon rarity, which is inconsistent with other items that had the Common rarity before being enchanted.

Steps to reproduce:

1. Obtain an enchanted diamond sword and an enchanted book
2. Compare both of their rarities

Observed result:
The enchanted diamond sword has a rarity of Rare, while the enchanted book has a rarity of Uncommon.

Expected result:
Both items have a rarity of Rare.