I have twice now completed the secondary contract to kill Aojee-Ei and both times the kill has not registered on my achievements despite the game recognising the kill as being completed.
It's a frustrating issue as the missions can only be attempted once a day and the random pool of contracts means it can be up to 2 weeks before the chance to complete this achievement comes around again, only for a bug to prevent it from being registered.
Is it worth bothering with this until there is a fix?
Also, I noticed there were two Aojee-Ei's in the instance (this second one I found on my way back from killing the first one. I killed both, even though only one had the dark brotherhood hand icon above him, and the game had told me the kill was completed) in case duplicate NPC spawns are preventing the completion of the contract.