It also saves the playlist in the order tracks were added - and doesn't give you any way to sort those tracks. You can sort by title or artist just fine when you're viewing your whole collection, but it doesn't work in playlist mode.
I finally figured out a kludgy workaround to get rid of the duplicated tracks. Playlists are stored as *.zpl in a format similar to HTML - might be XML, not sure exactly. Anyway, I opened it in Word, then copied & pasted the center section with all the track info into Excel. I sorted the track code there, then scanned the list manually for duplicates. Any time I spotted one, I flipped back to Zune and deleted the first version of that track I found.
