Q:

How did this duplicate question manage to be answered after being marked as duplicate?

This question on TSE was marked as duplicate on 2016/02/24 at 15:52:19Z. It was then answered on 2016/02/24 at 15:52:52Z, seconds after being marked as duplicate. 

How is this possible? Is there a delay between duplicate marking and closure? If so how long is this delay?

A:

That is possible since you are allowed to submit your answer if you started typing before it was closed as duplicate. This allows answers to come in minutes or even hours after it was closed. If you were connected it will disable the commit button but that can easily be reversed with some browser tools.
In my opinion, this is bad design, especially since it encourages bad answers to come through on rapidly closed questions.

