Windows 10
Version: 4.1.84.2021
DirectX 11
After pickpocketing Kagha out of spite when I saw her the first time and taking her key, I discovered her chest behind the bookshelves. I attempted to open it assuming the key would work. The key wasn't "used" and therefore it remained locked and I had to lockpick the chest to get it to open.
This may need to get fixed for those people who do not play with a rogue in their party and killed Kagha and got the key.