Problem
If the player finds two identical spellbooks he hasn't identified yet, and read-identifies one of them, the other one won't auto-ID when he finds it. This is unlikely to happen in the first place, but still possible with the most common books.

For example: I find a "parchment tome" on the floor, read it, and it teaches me the Darkness spell. When I find another spellbook of Darkness on the same dungeon, it's still a parchment tome (100s), even though I have it in my identified items list. When I pick it up or walk over it again, the game says "You pick up the spellbook of Darkness."/"A spellbook of Darkness (100s) is lying here." and it's identified.

How to reproduce it
See above. You need some luck, as two identical spellbooks for a spell you don't yet know must be generated in the same floor.

Notes
This is a very minor issue, considering the conditions required to trigger it and its "effect" on gameplay.