Comment 35 for bug 883485

I was about to say, this affects me too. But then I realized, that I'm already using a self-made script for mute-toggling. It wasn't working, too.

I googled a bit, and I found this:
http://askubuntu.com/questions/118675/mute-key-mutes-alsa-and-pulseaudio-but-unmutes-only-alsa

Short: Mute-Button muste Alsa and Pulseaudio, unmute only alsa. For umuting, we need to add pulseaudio on our own.

In a script, it should look like this (if you use the Master-channel):

#!/bin/bash
if amixer get Master | grep "\[on\]"; then
        amixer set Master mute
    else
        amixer -D pulse set Master unmute
fi