How to Reenable Bluetooth Audio Playback on Older Versions of iDrive [Video]
In the most recent versions, that doesn't happen anymore, but as not all of us have the latest BMW model in our driveway, we though it would be useful to show you how to solve such a problem.
So, to reenable the audio playback via Bluetooth you have to access the settings menu on the car's system, then select connections and then Bluetooth. A list of connected Bluetooth devices will show up.
Select the device you intend to use and then press the 'Options' button next to the iDrive controller. On the menu that will pop-up select Configure Device and then pick the Audio tab in the follow-up menu and then click OK. That's it! Now you're done.
In case we weren't clear enough, the video below provided by BMW should be a good guide!