Same thing is happening to me. It copies about 1500 songs every time I sync, which is pretty annoying. It never used to do that. I'm really hoping Apple will fix this in an iTunes (or iOS) update. I'm really busy, especially this month, I don't have time to go troubleshooting this. If it means I don't have to mess with it, I'd like to see a fix, even if it takes a month or two. That's why I quit using Windows and switched to Mac a decade ago - I wanted to spend my time using my computer, not fixing it. Anyway, much oblidged, Apple, if you can fix this issue at some point.
I too have this issue. Mine copies 552 songs every time. It's annoying. Will try to get to the bottom of it; don't know what I will find out...
My problem ended up being a Smart-Playlist. I removed it and my problem has been solved, it was a duplicate smart playlist I had created and had selected. While it was of 577 songs therefore I would expect I'd copy 577 songs each time, but it was 552; strange.