I have also encountered the same bug and have stopped playing for now until its fixed.
For context, its the exact same as the image above. I acquired the banners for the "Wardens warding" quest without killing any of the outcasts. When I went to hand it in she said I could open the chest as a reward, but she didn't need to give me the key because I had already opened it. Which is weird because you cant pick the lock it can ONLY be opened with her key and she doesn't give it to you!
Please fix!