I filed ubuntu bug 369762.
Ubuntu didn't think much of my bug. They sent me the following recipe to cure it, and marked the bug invalid.
1) Edit /etc/pulse/client.conf, and change "autospawn = yes" to "autospawn = no" 2) `touch $HOME/.pulse_a11y_nostart' 3) `asoundconf list' 4) choose the desired card from the previous command's output, and use `asoundconf set-default-card CARD', replacing CARD as appropriate 5) `killall pulseaudio'
https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/348353 mentions a recent kernel patch that routes all audio through pulse. I wonder if this patch is the culprit?