Start a new character, any race/class will do. Check identified items. Apart from whatever you have in your inventory, you will have 4-7 spellbooks identified for no reason at all. Of course your character doesn't have these spellbooks in their inventory. Works even for illiterate classes like a Beastfighter with starting Learning score of 3.

If it's a feature implementation which I missed and not a bug, I don't think it should apply to illiterate characters at the very least.

Present in both public R59 and public R60, but I've only noticed it today. Not present in pre23.
OS: Windows 8.1