I also flashed CM 10.1 on maguro, and ran the same scenario. It looks to me like mako isn't using REQUEST_SET_MUTE to enable mute when the button is pressed, whereas maguro does send a REQUEST_SET_MUTE with the value "1" to enable the call mute.
I'll spend some time looking at the Android/CM code and see if I can determine whether not mako is using an alternative mechanism...
I also flashed CM 10.1 on maguro, and ran the same scenario. It looks to me like mako isn't using REQUEST_SET_MUTE to enable mute when the button is pressed, whereas maguro does send a REQUEST_SET_MUTE with the value "1" to enable the call mute.
I'll spend some time looking at the Android/CM code and see if I can determine whether not mako is using an alternative mechanism...