I think there should be a Spotify mobile update for Spotify Premium customers to be enable them to keep there downloads on there mobile's when a Spotify update is available.

When a Spotify update is downloaded on a mobile phone a Refresh happens that takes off the Download technology on the mobile phone,when this happens the tracks are not able to play offline and the tracks have to be Downloaded again. 

It is an excellent idea that a Spotify premium customer can choose a track at random and just add it to his or her playlist without any fuss and Spotify on the computer should keep it that way.

Now it's up to the mobile part of Spotify to have a software update that enables the Spotify Premium customer to keep their downloads on their mobiles when there is a spotify Update.