iOS 6 insanity or RRE fickle?

Howzit everyone.
I've been reading the iOS 6 and iPhone 5 threads. OK, not all of them but you get my general drift. So then swiftly on to my issue. Dealing with an iPhone 4 running on iOS 6 I was merrily driving along the coast road listening to my tunes via Bluetooth when my phone rang. I pressed the green phone as I usually would only to realise that (1) the phone was not ringing through the speakers as per usual, and (2) the green button was not doing anything. I then had to pull a highly illegal manoeuvre and answer the phone using speakerphone. Upon reaching my destination I rebooted the phone (and the vehicle!) and made a call. Of course, I could not replicate the problem. Being the type of person I am I need to find a reason for the malfunction. Anybody else out there have a similar issue and, if so, how can I prevent this happening in future?
Thanks one and all

It sounds like the iPhone's phone hadn't properly paired up with the car's phone. Even though you had the two paired for music, the phone connection is a different 'service' over the Bluetooth connection. I don't think it's either the car or the phone, and certainly nothing to worry about, it's just Bluetooth in general isn't a flawless system.

Hi NightFox. I'm wondering though as the phone functioned absolutely perfectly since I took delivery and subsequent to the upgrade to iOS 6 as well as after I did the reboot. So the answer is totally random I guess. Thank you for your response and may your build date be confirmed real soon!