The browser will maintain the history if you opened the editor in a new page like HN does. For example, if I hit the back button or if there was a cancel button when composing this comment, I would return to exactly where I left off in the full list of comments.
I agree you can get into a slightly weird situation if you hit the back button after composing a new comment but your site would suffer the same.
I agree you can get into a slightly weird situation if you hit the back button after composing a new comment but your site would suffer the same.