USB sound driver mixer oddities

[Baldur Gislason]

I was running FreeBSD 7 for i386 on my PC and this year I upgraded to 8.2-STABLE on amd64.
I use a Griffin iMic USB sound adapter because the on-board audio in this Dell is ridiculously noisy.
After the upgrade, I can no longer mute the sound output, when I set the master volume and PCM volume both to zero
and/or select mute in the mixer, the sound just gets attenuated to a low level but not muted. I believe this
to be a change in how the mixer works in the usound driver, if not the sound system.
Is anyone else experiencing this behaviour?

Baldur