Phone contacts unstable

I have hooked up my iphone 4 to the in car system no problem, and the contacts have been transferred. However, when I leave the car and come back, the phone is recognised, but sometimes not the contacts. The display will show the phone connected but with nothing in the contact list. recent calls show, but not the list of contacts. If I then turn off the bluetooth on the phone and then back on, it will reload. Any clue if this is 'normal' or is there something I am not doing correctly?

 

If I take the time to reload the contacts by turning the Bluetooth off on the phone and then reconnecting, the contacts will load and then stay while driving, until I stop again. Then I have to go thru the process once more if they become disconnected after stopping etc. This is inconvenient if I am running errands with multiple stops, while still wanting to make calls while underway.