It's simple, and apparently was brought up during the beta testing and this is actually the SOLUTION to the problem. Originally if you edited a post with a link, the auto-parser would reparse the already parsed link. So you'd end up with a link within a link within a link. So they just made it so that on editing, the auto-parsing doesn't happen, it leaves any existing links as they were and any new links don't get parsed.
I don't really understand why it wouldn't be simple to make the edit function only parse the new links, since it's obvious which ones haven't been parsed yet (no L /L tags), and when you make a new post with both an unparsed link and a link using the button for text/link, it parses the regular link without affecting the already tagged link. (This was brought up in the beta as well but never got answered as far as the person I was talking to saw.)