Spotify on Mac and iPad: Not all owned tracks are synced to the iPad

[aroenatmac]

Hi, this is what I have done: Made playlists in iTunes, all music is owned (either imported from CDs or purchased in iTunes store). Then imported some of those playlists to Spotify (premium account) on my Macbook Pro. I have noticed that some of the tracks appear as grey, while others appear as white.

I have then logged on to Spotify on the iPad and selected "download playlist- yes" - for each of the playlists I want to be available offline. The process of syncing tracks is performed, but not all tracks are synced. There doesn't seem to be a full correlation between which tracks are grey on the Macbook and which tracks are not synced onto the iPad. Can someone explain why tracks that I do own are not synced onto the iPad? And what does white and grey tracks indicate on the Macbook?