Well, I got to the point where I could test this on my single player game (was waiting for the AI personalities before restarting it) and... The teller still regenerates her books every level. I got her unlocked at 5, bought books, leveled to 6 and she had a new set to sell.
It appears this bug/"exploit" was not fixed at all.
Maybe it only works on game where you haven't unlocked her, yet? Or, perhaps it only applies to new games, not to existing saves.
