There seems to be an issue with dungeon quests that are completable with clicking on the questlog.
I have experienced this issue in some dungeons (Deadmines for instance) where I wasn't able to turn the quest in. The storyline window would open but it stayed empty and I wasn't able to turn that quest in.
I deactivated the addon for that. Sadly, there was no error-message or anything to report back to you :(