When a question has pending duplicate votes, a message should be displayed above the answer form.
Warning: this question is a possible duplicate of [...], are you sure you want to submit an answer?
Example: I vote to close this question as a duplicate. The first answer was a few seconds before my vote, but still new answers were added 3 and 7 minutes later. They're good answers, too, but they should probably have been posted to the original question as to avoid content fragmentation.
I believe it'd be useful to see such a message appear while writing an answer. If that person decides that the close vote is incorrect, he/she can still continue to write and submit an answer.