Actual behavior
- Enable the "New wikitext mode" as a Beta Feature
- Go to: https://en.wikipedia.beta.wmflabs.org/wiki/Talk:Cats
- Click "Reply"
- Start writing a comment
- Click "Edit source"
⚠️ 6. The full page editor is loaded; comment draft is lost
Expected behavior
- Enable the "New wikitext mode" as a Beta Feature
- Go to: https://en.wikipedia.beta.wmflabs.org/wiki/Talk:Cats
- Click "Reply"
- Start writing a comment
- Click "Edit source"
✅ 6. The browser displays a warning message [1] alerting contributors their draft comment will be discarded if they proceed
- Browser warning message: "Leave site? / Changes you made may not be saved."
Additional context: T240259#5873772 + T240259#5872964