if i make a "new" change to my music section while it's stuck in "finishing" mode there, it syncs quickly with the change and stops.
i also tried this with the apps section, deleting or adding and it didn't work.
i also tried making the same change twice in a row and it didn't work.
so adding say one new song to yr iphone or deleting a playlist, both worked.
my problem seems to be related to music.
if i just uncheck "sync music" the problem goes away completely. with this unchecked i have plugged and unplugged my iphone multiple times without the endless syncing issue.
obviously this isn't a great fix, i'm only posting to help narrow the issue.