I have seen lots of wierd things happen with the disc groups are placed within the root web. This practice causes some issues with file sharing, and bad things usually result.FP disc groups should always exist as separate subwebs. When you create them, the wizard gives you the option of going newest to oldest or oldest to newest. This works with subwebs, but it doesn't work if you are trying to ad the disc group to the root, and you have previously added a disc group with the other ordering rule.
Take a look here for more on subwebs.
http://www.outfront.net/frontpagesubwebs.htm
