I just created an answer. I started editing the answer just before the 5 minutes were up, and saved it just after the 5 minutes were up, so the system substituted 'added 231 characters in body' as the edit summary comment (the 'editorial' comment, explaining why the change was made). Normally (meaning 'in times past') you could reset the text of the comment by editing again and changing the comment. This morning, it won't let me do that.
This is not an improvement — please revert to the old behaviour where the edit summary comment can be edited too.
Re-investigation
TL;DR — reproducible, but possibly intermittent.
(First seen with Firefox 23.0.1, reproduced with Chrome 29.0.1547.65, both running on Mac OS X 10.8.4, but on two different machines.)
I just created another answer to the same question as before, and I've now deleted it (so only 10K users can see it at all).
The sequence of operations I did was:
- Create the answer.
- Within a minute or so, edit the answer, but do not set the edit summary to anything, and do not save yet.
- When just over 5 minutes had elapsed from answer creation, I submitted the edit. It got an automatic edit summary 'added 606 characters in body'.
- Immediately review changes to answer — to see the automatic comment.
- Return to answer and edit it again (within a minute or so), and try to change the edit summary (only).
- Save the edit. Rereview the changes — automatic comment not changed.
- Return to answer and edit it again this time editing both edit summary and answer body.
- Save the edit. Rereview the changes — automatic comment not changed.
- Return to answer and edit it again, changing both body and edit summary.
- Save the edit. Rereview the changes — this time edit summary did change!
- Return to answer and edit it once more, recording disbelief.
- Save the edit. Rereview the changes — and the changed edit summary is still in effect.
I deleted the answer (since it was anything but an answer to the question), but 10K users can see what I wrote as I was reproducing it.