(Only posting this here because there isn't a dedicated forum bug reports forum.)
This is yet another extremely frustrating forum bug. If you're in the process of composing a reply to a comment and the comment is edited, your reply is deleted. This can be extremely annoying if you were composing a long reply.
*Sometimes* your reply will be saved by the forum's auto-save mechanism (so if you press Reply again, the contents will be there). Other times, it won't be.