Reproduction steps:
- Turn on the Prompt me when entering a blank edit summary preference.
- Start editing a page in either editing mode (i.e. visual or source).
- Make some change to the text.
- Provide an edit summary.
- Switch to the other editing mode. Result: My edit summary is still filled in. [OK]
- Make another change to the text.
- Click Publish changes. Result: Warning "Reminder: You have not provided an edit summary...." is displayed. [BUG]
- Click Publish changes again. Result: My edit summary is saved together with the edit. [OK]
Possibly related to T144906.
Version: 1.41.0-wmf.1 (4de0415) at cs.wikipedia.org