Apple phone/radio bluetooth disconnect turns on phone speaker (music)

Question

I recently added an automobile radio that connects (streams music & phone call ops)  without any concerns. However, when I turn off the functioning paired radio device the music, whether itunes, pandora or independent radio stream for actual examples,  soon starts playing via the iphone speaker as I walk away from the vehicle. It happens every time and can become frustrating and embarrassing as I need to get past the security lockout in order to stop the music source (pause play) which is usually loud.
I have numerous bluetooth devices, radios and speakers that previously worked fine, unlike this instance, and I think they continue to do so... Which is why I expect the same.
Any suggestions?

Answer 1

See this veeeeeeeeeery long thread.
https://discussions.apple.com/thread/3404857
It's an issue with hundreds of phones.  Some claim it's software related, some hardware, some say it's a mixture of both.
Some people have had temporary success with quitting the Phone.app / restoring as a new phone / restoring from an iCloud backup / disabling Siri / toggling speakerphone on & off...
Unfortunately all of the above only been temporary, with the problem recurring again after a few calls, or a few days etc.
So far the only solution that seems permanent has been to replace the phone.  But even so, it's the luck of the draw to recieve a functional phone, and not another faulty one.
I'm completely annoyed as there is no Apple Store near me...... and Apple haven't even acknowledged the issue, despite the above thread being 34 pages long, as of writing.