what's the build number ?
Mine is JOP40D
As suggested before , it's an issue with 4.2.1 , in fact it's been a problem with Jellybean full stop, ICS and it worked fine for me.
Your issue is the same for me , a bit hit and miss ( i-drive version)
To work around ,If you turn bluetooth off on your phone before you get in the car , then turn it on when you start the car and you will be ok.
Q. Have you changed the name of your phone recently ?