Kenwood knows there is an issue, as do most at this point. (I don't work for Kenwood, but have talked with techs there, and there is a post on here from them too).
I've tested my 4 running 6.0 on a few units and there are issues, and they vary from brand to brand and model to model (tested JVC, Pioneer, Kenwood so far).
The OS has been offical for a few days, give people at chance to test things and see what's up. If you want to get mad at someone the priority levels would be:
1. Bluetooth Association for having so many variences and options within their standard - read it, it's brutal how many optin's and out's their are. As well for not building in better legacy support assurances into their spec.
2. Apple for not providing hardware and software beta's earlier, and with longer test windows
3. Manufactuers for not being more proactive in testing this stuff - but with so many models and phones etc - it's tough to do without full completion of #1 & #2.