Hi,
Depending on your MMW/MMA versions it has different algorithm to check for changed content and in most cases it will resunc files that have changed Album art or tags other embed metadata to enhance browsing and searching on the phone.

MMA 2.0 in Developer Pre Night builds for UI testing things should be different and more reliable in detection of changes.

Also, if it constantly resync whole library it would be great if rise Support ticket so that we can get into more details why it is happening and how remedy that?

I am trying to sync playlists only over wifi. I have it properly set up with only the playlist item checked for syncing. I was able to do this a few days ago and it worked fine. I needed to resync my playlists again so I did it and now for some reason it syncs all of my songs and I only want my playlist synced not all the songs in my library. I have it properly configured with only the playlists selected. Why is it downloading all of my songs when I just want playlists downloaded?