We've actually been looking into this problem today already. We haven't found the problem yet, but what happens is for some reason, sometimes for some people, all tags are removed from the post (so it doesn't have a place to
show up). Forums are just tags in our system. Will let you know what we find out.
It only happens when you edit the post (EditComment).
Also, your "render view generator" strips the "border" attribute from "table". When edit, it's there, just not there in render view.