I just picked up my new BMW 2013 5 series and have the exact same 2x speed issues. I have done some additional experiments and have noticed the following. Hopefully there is a software upgrade or a way to turn off the double speed function as it was a pointless addition to begin with.
Seems to impact the following:
1. All audiobooks from Audible.com
2. Some Podcasts. - specifically - it does NOT affect "Manager tools" for some reason but does for HBO audio podcasts.
3. Does not impact music at all. - Seems the pointless (speedup/slow down) function is only available for Audiobooks and podcasts and spoken word - which is why only these are showing symptoms.
Cures:
I tried "fooling" the system by converting Audiobooks and Podcasts to "music" media in the ipod - thinking it would disable the speedup/slowdown capability and solve it. It did not. Bummer.
Using the BMW supplied adaptor fixes it - but due to it being a different type of delivery system - it does not display the cool album art on the screen, which I kind of like - Bummer.
What does work but it is a hassle - put all your Audio books and podcasts into a playlist and add 1 or 2 "anchor songs." When you arrive at your destination and listening to a book - go to the playlist and select the song. Once playing turn off the car. Next time you turn on the car - it will start on the song and you can then scroll down in the playlist to the book you were listening to.
Same goes for Podcasts - if you know one (manager tools for instance) does not to this - click on that podcast when you stop the car and then return to the one you were listening to when you get back in.
This is my cure so far - but really Apple - make an update for that book thing allowing you to disable. When you deal with companies such as Apple and BMW - you kinda expect to be paying to NOT be annoyed by this kind of thing.