I'm not sure this will be useful as I can't see how AH would have affected it, but here's how to mute mic playback in Windows (if your headset is not USB):
Open the volume control. Click Options Properties. Make sure the Mixer device is your output, not input, and "Playback" is selected, not recording. Under "Show the following volume controls" make sure the input that your mic connects to, mine is "Rear Pink In", is checked. Then make sure the Mute for that input is checked.