Ubuntu 12.04: Bluetooth headset A2DP works, HSP/HFP not (no sound/no mic)

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http://askubuntu.com – My Philips SBH9001 headset pairs fine using Ubuntu 12.04. In the audio settings it's properly detected as A2DP device and as HSP/HFP device. Hardware: Thinkpad X230, Ubuntu 12.04 64bit, Kernel 3.6.0-030600rc3-generic (build from Ubuntu mainline repo), Bluetooth device is USB-Id 0a5c:21e6 from Broadcom, Headset is a Philips SBH9001. Playing audio in A2DP works just fine out of the box, but when switching the headset to HSP/HSP mode there is no sound nor does the microphone work. When connecting the headset, /var/log/syslog shows: Aug 25 21:32:47 x230 bluetoothd[735]: Badly formated or unrec (HowTos)