I have a related issue with my car Nissan Rogue that came up after ios 7 upgrade.
I use Spotify and other music apps to listen to music when driving. My car has an ipod/usb aux input that I uses to play the music on my car's audio system. Until my ios7 upgrade, I was able to play music from my the music apps playlists to my car's audio system - which worked seamlessly
a. my car audio system would display the song info
b. transition from one song to the next one in the playlist was fine
c. i could control music - play/paus/rev/ffd with my car's steering mounted audio system control.
However, since the time I have upgraded to ios7 - I am facing a glitch. Everytime I play music from the app using the usb aux input - it just plays just one song that I select on my playlist on the app and the music transitions back to my iphones music playlist, instead of continuing to play music from the app. Also, when I use the car audio control to skip the song, insetad of selcting next song from the app it goes back to my iphone playlist.
Any thoughts on how to resolve this? Anyone facing similar issues.