Playlist on iPhone with IOS 8 doesn't work via USB

Hi all,

My wife has a 2011 Prius IV and she used to be able to play songs in her iPhone playlists via USB. Recently I upgraded her iPhone to IOS to 8.1 and now she told me she couldn't play any song in any of the playlist anymore. Here's what I have found out so far:

1. Everything works if she goes to the iPhone Music app, selects a playlist, and plays the songs.
2. If she tries to play the songs by using the touch screen control of the navigation system. She is able to see the playlists in the Playlists tab, she's also able to see the songs if she chooses a playlist, but no music is played once she selects a song and the song list just grays out. If she touches the OK button after that, she'll be back to the USB tab but there's no song information. Now if she presses the Menu button again, she'll be back to the Playlists tab and this time there's no playlist.

Sometimes she will get an error saying the device is not connected, but she doesn't remember what she did.

Is there anyone else who has the same experience? I wonder if this really has to do with the IOS upgrade.

Thanks,
Tang