Can't use Macbook Pro built-in mic when a headset with mic is plugged in

Hi forums,

Referring to the topic above I can't use my built-in microphone when a headset with microphone is attached.

I went to System Preferences>Sound>Input but the built in microphone isn't listed as shown in the picture below.



Only when i unplugged the headset the option to select the built-in microphone is available.

I don't mind if I have to use software as a workaround. This has been around since I first bought my mac.

I'm using a Macbook Pro 13 inch (mid-2012)

Slightly off-topic
Is it normal for apple to delete their own replies on their support community website? I posted there last time a community specialist answered my question i replied back that it isn't the solution and gave him a picture of the above. Several hours later the reply was gone. I have pictures of it if you wanna see.

It goes through the Audio port

I've tried it with different headsets with a mic it's still the same.

Some additional information :
I'm running the latest version of OS X 10.8.3