It is a problem in the blue tooth stack***. There is a bug. Reboot your phone when you leave your car. Problem solved.
(*** Network protocols stack up. You have to depend on other people (Companies) to provide an interface. Some programmer screwed up and isn’t clearing the connection to a lower level in the stack to allow it to reset.)
When you say reboot can I just turn it off and on or do I have to remove the battery too? What a pita%^&^*&^