Comment 27 for bug 871611

additional info that may be of interest:

on headphone insertion (2./4.) the "Speaker" "Mute"

- is automatically set to mute enabled, but
- has no effect (headphones are not muted either way)

and on headphone removal (3.) the "Speaker" "Mute" is enabled again

- another related bug just found: muting the "Speaker" (if headphone is removed) won't make it produce any sound again (even after alsa force-restart) (headphones still work on insertion)
  (somehow the master volume seems to be effected by this as well because it will jump to 0% and muted if one plays with the "Speaker" or "PCM" volumes in Gnome Alsamixer afterwards)