I have a Tuneair bluetooth device plugged into my car stereo, under IOS6 when i plugged the Iphone 5 into the cradle, it would always go to bluetooth to stream music. I would have an option Speakers, Tuneair or through cable connection. I have a HDMI/ lightning AV adaptor and only use the aux in as a charging cable.
I have upgraded to IOS7 and now notice that when I select music, it does not give me an option when it is plugged in, unplug it and everything works fine.