Not sure if this is a bug, but it is a problem

If Haathbar leaves the library and tries to come back, then he and guard infinitely displace each other, so purchasing anything becomes impossible

I hate to be the one to ask, but have you got a savefile? All good if not

Isn't there a displacement priority value for creatures? Maybe we could just increase it for all shopkeepers to stop guards from (easily) displacing them.

Sorry, but that savefile is long gone!
Also, I just remembered, but this screenshot is from LIVAN, but I quickly fired up a 0.58 wizardmode and replicated this. You can do this pretty quickly in wizardmode too, but if you still need it I could make a save for you

Does taking the items from the bookshelves count as stealing if he isn't in the shop?

It's the same as using invisibility, breaking line of sight when taking items makes you unable to purchase the items

I guess i will clarify my question, since I will not be able to playtest this myself anytime soon, if you take an item while the shopkeeper is out of the store and cant see you , will it make him hostile

It might. Stealing makes a check with your Dexterity and if you fail, the whole shopkeeper's team gets hostile (like in Attnam it's not just Haathbar who gets hostile when you steal from the librarty).

Oh no kidding.. I had no idea you could successfully steal with high enough dexterity