See the discussion here.
The gist:
We no longer pin the accepted answer (with the green checkmark) to the top of the list of answers. By default, we now sort strictly by votes (descending order by highest score), and the accepted answer's order in the list is based on its score.
[...]
Seeing that some sites do not want to unpin the accepted answer, we decided to move forward with the status quo and not to change the default behaviour on existing sites. If you think unpinning the accepted answer on your site makes sense, please do the following:
- Start a meta discussion on your per-site meta.
[...]
For reference, as of Oct 1, 1:15am UTC, ECON.SE has 215 questions whose accepted answers are not the highest voted. This amounts to about 2% of the currently answered (or more precisely, non-unanswered) questions.
Edit:
Feel free to post differently worded answers, in the end we will only aggregate the Yay or Nay parts.