Speakers unmute after unplugging headphones

After muting my Mac, and removing my headphones, the sound of the speakers is not muted anymore.

Very annoying if you're sitting in the Library and you accidentaly remove your earbuds. I actually only experienced it after upgrading to Mountain Lion, but that might as well be because I just didn't get into this situation yet. Is this a bug?

I want one overall control for both the headphones and speakers, so that when I mute my volume for the purpose of taking my headphones out, it doesn't switch back on automatically. Is that possible?