This is a very minor bug concerning the first conversation with Kana. the steps to reproduce it are:
1) Go and talk to Kana the first time you see him before entering Caed Nua. Don't invite him to your team.
3) Kill Maerwald.
4) Talk to Kana again.
Kana will treat you as if you just met, telling you again about the book. Whatever marked the first conversation had taken place seems to have been resetted after killing Maerwald.
I am not sure whether resting or not made any difference. I rested twice between talking to Kana the first time and killing Maerwald.