My bad.

By the way: the Set Playlist Order menu option still works in the root playlist.

If you'd prefer to have your playlists in a custom order, one possible workaround is to rename your root playlists as, e.g, "00 Genres", "01 Artists", "02 Special Playlists", "03 Soundtracks", etc., and then use the Set Playlist Order function. Then change the names back.

You might still have a gap in the numbering where the "Unattached Items" playlist would be, but it's a minor irritation (IMO).

Alternatively, use JEmplode.