Macs have lost the ability to use external microphones after a hardware mute

Hello,

I recently discovered an issue with the microphone of my Sennheiser headset and my newly purchased 15" Retina MacBook Pro. I use an adapter to combine the two 2-contact phone connectors from the headset into a 4-contact phone connector. One clever feature of this particular headset is that the microphone broom also acts as a mute switch: raise the mic and it is disconnected, lower it again and it is reconnected.

This setup worked flawlessly for many years with my previous 17" MBP but with the new one, trouble started. Connecting the headset with the microphone lowered works as before, the mac recognizes external speakers and microphone and happily proceeds to use them for audio output/input. Muting the microphone also works as expected, since that functionality rests with the headset. Unmuting it, however, doesn't work anymore. The MBP still recognizes the existence of an external microphone but no signal is received. Disconnecting and reconnecting the entire headset restores the microphone signal. This is 100% reproducible.

This is not limited to the Retina MacBook Pro and my machine does not have a hardware defect. I went to an Authorized Apple Service Provider / Reseller to test this with their showroom machines. Every current Mac except the 13" non-Retina MacBook Pro and the Mac Mini showed the same inability to use a microphone after a hardware mute. Even the $3,000 Mac Pro disappointed in this matter.

A quick search lead me to the Cirrus 4208-CRZ audio processor, which is in the Retina MBPs, MacBook Airs, and the Mac Pro, as well as the Cirrus Logic 4206BCNZ. which can be found in iMacs, as suspected culprits.

With this problem, the mute functionality in my headset has turned from being clever and useful to my biggest annoyance. When I Skype with someone and want to mute my microphone to prevent them from hearing me drink, sneeze, cough, or blow my nose I have to break my habit of simply raising the microphone and remember the key for the software mute which still leaves the microphone in the way.

I already sent a bug report via the feedback page and the AppleCare representative I contacted aout this issue is waiting for a response from the development department but I fear that this will simply be ignored or brushed off and swept under the carpet as 'not fixable with a software update'.

How can this slip through QA? How come that I couldn't find any report on this? I can't be the only person using a microphone with hardware mute on a relatively new Mac. A similar mute functionality is present in many headsets.