Since I've got my 4S I've created a smart playlist to use to sync music to it, but it has twice disappeared, and thus deleted all the music from the phone when I next sync. Very annoying, as it takes half an hour or so to sync it back on again! Any ideas?? Win/XP machine, BTW.
I've been paying attention when I sync, and what seemed to happen is that the playlist had disappeared from the phone before the sync (presumably the sync then deletes it from iTunes, and as it's the playlist to sync with, then deletes all the songs from the phone!) Very annoying! I'm sure I didn't intentionally delete it from the phone, and I never use it on the phone (as it's effectively all the music on the phone).