Multimediakey XF86AudioMute mute sound but doesn't re-launch it

Lubuntu 12.04 : the Multimediakey (of the keyboard) XF86AudioMute mute sound but doesn't re-launch it. It is necessary to manualy clic on the icon to re-launch sound.

The solution is to modify the file ~/.config/openbox/lubuntu-rc.xml.

<keybind key="XF86AudioMute">
     <action name="Execute">
        <command>amixer -q sset Master toggle</command>
    </action>
</keybind>

should be :

<keybind key="XF86AudioMute">
      <action name="Execute">
          <command>amixer -D pulse set Master toggle</command>
      </action>
</keybind>