Help Navigate and Music Problem?

[mcknigs]

I'm taking a trip across town to someplace I've never been. I fire up the navigator and give it a location. I plug the Droid's audio output into the car stereo to better hear the directions. I start driving. I hear the directions. The map continues to update on the screen. Getting bored with the silence in between directions I open the music app and start playing music on party shuffle. I open the navigation map again. The music plays, periodically being muted in order to hear the directions -- that's fine. However the map stops updating. I'm now depending only on the directions to know what's coming up. This has happened twice now.

Does this happen to anyone else? Is this a bug, a feature or something I'm doing wrong?

-Scott