Recently, without seeing a previous answer I posted essentially a duplicate of this answer, and that duplicated was accepted. I posted in error, yet apparently my mistake was appreciated by the questioner.
As an acting moderator I have the power to enforce whichever outcome I desire, but I feel that it would be disrespectful to the questioner to delete the answer he found most helpful. (It is also probable that such an answer is of value to others.) On the other hand to let is stand seems to go against the unwritten code of self-deleting near-duplicate answers when someone posts first, and therefore disrespectful the the original answerer.
Therefore I ask:
What is the best way to handle a situation like this?
Does a moderator have any role in this if he was not one of the actors?