That's strange, from what I've heard is that iPhone 5 and iOS 6 work even better with BMW. I have an 05 545i and I used an iPhone 5 np, don't think there are that many changes in the iDrive. I have since broken my 5 and now am back to my 4S, but my 5 worked great on mine for the 3 weeks I had it. Hopefully others with a similar year/model can chime in.
"You can't trust quotes from the internet..." Benjamin Franklin Jan. 3, 1782