I guess more explicitly, it's sorting by author, but there are no section headers for each author. Not sure if that constitutes a bug or not.

This is discussed a bit in ticket #1180 (Mailman archive pages on lists.fedoraproject.org are f*ugly). The archives use the default archiver Mailman provides, which is a bit less featureful than the MHonArc archiver used on the redhat.com Mailman instance.

Whether it's worth the trouble to convert things to MHonArc I don't know. I've never used either set of archives extensively enough to notice the differences. For anything more than sharing a quick link I tend to use my local archives or one of the various third party archive sites, which do a better job than either Pipermail or MHonArc IMHO.

pipermail lacks the functionality and I Honestly feel its not worth switching to mhonarc Im on a list that uses the default mhonarc setup and its worse than pipermail. I belive it does offer greater functionality but you need to spend some time to set it up to suit.