Damn mine just will not do that.
For example I have a Nokia N900, my wife has a Nokia N97 and I have an old N82. All three are apired with the head unit.
Yesterday I sat in the car with the N900 on and the head unit paired just fine. I then switched off the N900 and switched off the cars ignition as well for good measure. Switched on the N82 and the car and started a drive. After a half hour the N82 was still not conneced to the head unit.
On your pioneer would the N82 have connected in that scenario? If so then I will carry on testing and trying.
Thanks