It sounds like you're describing two different issues:
1. Audio automatically switches to USB. That part is not a bug while we ship 'module-switch-on-connect'. So if it's annoying just remove that module.
2. "Despite seeing the USB device as the current output device, I still hear sound from my line-out." - That sounds like what we're currently tracking in bug 1866194 so let's use that for now.
Ben,
It sounds like you're describing two different issues:
1. Audio automatically switches to USB. That part is not a bug while we ship 'module- switch- on-connect' . So if it's annoying just remove that module.
2. "Despite seeing the USB device as the current output device, I still hear sound from my line-out." - That sounds like what we're currently tracking in bug 1866194 so let's use that for now.