I collected all four books from Undercaverns and turned them in to Navin (all at the same time), but when I hail her I still get text about how Gavin wants books. The others in my group turned in their books as well but were prompted to get a codex afterward. They said they had turned the books in one at a time, so perhaps that is where the problem began. I have tried turning them in individually, but I didn't get the reponse from Navin that I got the first time - she just hands them back. What can I do to get her to prompt for the codex?