A bug was reported where editing a poll option and then reselecting that choice breaks poll percentages, resulting in inaccurate results. JP_ demonstrated the issue with a poll, showing how their selection caused the percentage to increase to 200%. Mittineague suggested a potential fix would be to prevent editing of poll options after any vote has been cast. However, zogstrip claims this issue was fixed a while ago.
AFAIK Polls currently allow edits based on a site setting edit time window.
I guess the easiest fix would be to also not allow editing after any poll option had received a vote,