Cannot change (add) an edit description after making the edit [duplicate]

Question

This seems like a bug to me, but it may be that I misunderstand the feature.

I recently made an edit to an answer (it was in fact a rollback that I deemed worthy), and as per usual I forgot to give a reason for my edit. Normally this wouldn't bother me as any edits I make are usually obvious as to why they have been made, but in this case (a rollback) I felt it important to give my reasons why.

So I clicked the "Edit" link under my rollback - which by the way had a current auto-generated description like "rollback to revision 2" - I added in my "Edit Summary" and then clicked "Save Edits". It submitted fine, but the description was not changed. I tried this a second time with the same results.

Is this the expected behavior for this action? In which case I assume it's because there is no change to the code/title/tags?

If it is working "as designed", then I would suggest that the user is notified with a warning that this edit will not have any effect, giving the reasons why.

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I think the best way to replicate this issue/query is as follows:

1. Go to the edit history for a post you have previously edited
2. Click the "edit" link under the heading of your edit
3. Change (or add) an "Edit Summary"
4. Click "Save Edits"

It should appear successful (it submits fine), however no change will have been made