iPhone sync creating new playlists instead of synchronizing

I mainly listen to music with my phone and will add songs to playlists then when I "sync" with my computer, instead of just adding the songs to the playlist it creates a whole new playlist with the same name but numbered. Sometimes it will create two or three new playlists that I then have to figure out which playlist has the added songs and then delete the playlists from both my phone and computer. This is not what SYNC means, sync is short for synchronize, meaning it should synchronize the playlists not create new ones. This has bothered me for over a decade so I know it's one of those awesome "features" that can't be turned off but if someone has a workaround I'd love to hear some solutions.

[Re-Titled by Moderator]