Having this same issue too
So it seems like it's in iTunes across both Windows and Mac platforms.
Fairly annoying and it only seems to have started in the last month or so.
I notice the duplicating issue when I sync an edited playlist.
Say I have a playlist named "MIX - Rock" and it was created in iTunes
In iTunes if I add or remove tracks to that playlist, then sync, I get 2 playlists in both and on launchbar
MIX - Rock& MIX - Rock 1
After comparing both the one with the correct ORIGINAL name has my added tracks.
The MIX - Rock 1 seems to be a copy of the former playlist before I edited and synced the changes.
I've been deleting the extra playlist copy but thought I'd try and look for a solution, ended up finding this thread.
So at least I don't feel alone now