Comment 3 for bug 491055

Please, someone take a look at this.

I once more describe how to trigger this one:
1. Connect USB speakers (pretty cheap these days)
2. use gnome-volume-control to change output to USB speakers
3. see how your laptops volume buttons work good with these
4. disconnect USB speakers, volume comes from the internal speakers
5. test how volume buttons are still good
6. reconnect USB speakers, sound comes from these
7. but volume buttons still drive internal speakers' volume, so have no effect
As a workaround you need to open gnome-volume-control again (you probably had it closed),
and from output choose internal speakers (which causes the sound to jump to these) and pick USB speakers again. Now everything is as expected. While including the jump of sound, this is a lousy workaround.

So what should gnome-volume-control do? Every time a *previously used*, but simply disconnected (and not chosen to be unused before that) device reappears, it should be selected as default device. Since this is exactly what pulseaudio does, you don't even have to trigger the output change, it is done in pulseaudio anyway (not sure if this is a good or bad thing).