Why does music start playing when navigator is activated?

For some reason, whenever I activate Apple's native map navigator or Garmin USA (the two Navigation Apps I use) on my iPhone 4S my music library is automatically accessed and songs start playing from the library in a random fashion. I am listening to my iPhone through my car's (Prius) sound system via bluetooth when this occurs. I have not tried this outside the car. I do not have the music app, or any music app, running before activating the navigator. I also do not have any music apps in the "recently used apps" bar before activating the navigator. Once music is activated, I can get the music to turn off by closing Apple's music app in the "recently used apps" bar...where it now magically is alive.

I would prefer to have manual control over when music plays in my car and not have it automatically come on when I activate a navigation app.