Driving Mode isn't working as expected on Samsung Galaxy SII
It could be possible that the contacts have been entered incorrectly, or it could be a bug with your version of the car mode app.

Please ensure that none of your contacts are duplicated, and also please ensure that the numbers are correct (you may need to add/remove the country code).

Another reason could be due to the country code being displayed when the SMS/Call is incoming, but not being in the contact.