Comment 29 for bug 878986

David Henningsson (diwic) wrote :

I think the problem is the following:
1) You mute Master
2) Pulseaudio picks the change up, thinks you want to mute and mutes itself, as well as the other ones just to ensure you're really really muted everywhere.
3) You unmute Master
4) Pulseaudio does pick up that change, but at the same time, since other mixer controls are now muted, PulseAudio does nothing.

Btw, by controlling PulseAudio instead of amixer, your keyboard shortcuts will work correctly.