Comment 17 for bug 436792

Pulseaudio is often at the root of sound related problems, especially since MythTV doesn't support it well yet.

To those of you having the killed sound, what window manager are you using?
Asked another way, did you install the myth packages as add-on's to an install that wasn't originally Mythbuntu?
Mythbuntu defaults to Xfce which isn't as ingrained with pulseaudio as something like GNOME. If you are using GNOME, it might explain why there have not been widespread reports of this.