Scenario. Person answers a question with a reasonable answer for the question as it appears and it gets upvoted. The OP comes back later and changes the question so that the answer is now clearly wrong. You answer the updated question, again correctly but based on the updated question, but your answer appears after the other answers. Do you downvote the other (incorrect) answer so that your (correct) answer appears above it in the vote list?
Does your answer change based on whether you've edited the question to clarify it (thus making the other answer wrong)?