This is rather specific to quote whole post, and I would argue users should be discouraged from using that button in general… it is better to select just the text you want to reply to, and use the quote text button that appears over the selected text.
It is also somewhat specific to import cases where we imported as HTML, for future conversations it is extremely unlikely people will type their new posts in raw HTML.
Not opposed to some kind of workaround, but context is everything here.