In a nutshell: When using the "Quote message in reply" option on the quick reply box, it should quote the message as it appears on the page, not the potentially edited and corrected version that is in the database when the quick reply message is submitted.
Click "Quick reply"
Check "Quote message in reply"
Write your response
Submit response
Quote is pulled from the database and prepended to the reply
The problem is when the user I'm quoting edits their post somewhere between #1 and #5, which causes me to quote a version of the post that I was not replying to (often causing my reply to appear nonsensical). Instead, it should be:
Click "Quick reply"
Check "Quote message in reply"
It extracts the quote from the DOM or retrieves it from the server via AJAX and inserts it at the beginning of the edit box (whether or not I've started typing my reply) (If retrieved by AJAX, and it's already been edited, then I can see it and choose not to reply at all if my reply no longer applies)
Write reply
Submit it
An added usability benefit, is that users can trim or split up a quote they are replying to instead of simply having it added to the beginning of their post.
I chose to submit this as a suggestion and not a bug, since it would almost surely be marked as "working as designed". But it could be considered a bug, simply because if I quote a post, I (as a user) expect to quote what I'm seeing, not some future version of the post.
This might not seem like a big deal, but I've actually had this happen to me a surprising number of times, where I quote a post and correct something, but come off looking like a jerk because I'm accusing someone of an error that's not even in the quote within my post.
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