What is the proper way to sync owned music to IOS?

[lensgrabber]

Example...  I have a album from Def Leppard.  There is a playlist called "Def Leppard" and the songs are synced from my local library to the Mac desktop app.  The app plays them fine.  I do a offline sync to my iPhone 6+.  Everything works great for a few days then on the iPhone some of the songs get replaced with "live" versions out of Spotify's library out of the blue.  So when I go to play the music I get hit by crap versions instead of what I originally synced.  It sounds silly but this is really ticking me off.  Am I doing something wrong or is this a known "feature" for spotify?