When connected to my car dock, Spotify does not send the correct track information to the vehicle's audio system. It seems to work for the first track, and then gets stuck and does not update until you get to a Spotify advertisement. I actually chose to downgrade from Spotify premium so that it I would get the right track info some of the time! My wife gave up and chose to use Pandora, which does not have this problem.
I have tested this with both a 2010 Porsche Cayenne and 2011 Range Rover Sport on an iPhone 4S.