It may not be a bug, but I don't believe that a single Librarian should give out the same enchanted book as different trades.
Environment
To recreate, Have a villager, place a lectern. Must be a lectern, because this is only achievable by Librarians. Trade with Librarian until all trades are unlocked. Check enchanted book trades. If none are the same, get a new villager, and start again. Must be a new villager because only Novice level villagers will become unemployed when their work station is broken
Duplicate of MC-71354