Comment # 26 on bug 972238 from ill lume

Yes. I stop all apps that are playing audio. I mute it, then tell something to
start playing audio, and it unmutes, on flat volumes and no flat volumes. If an
app is playing audio and then I mute it while it is still playing audio, it
seems to stay muted until nothing is playing audio, but will then unmute once
something starts playing audio, so there needs to be nothing playing audio,
then tell an app like music player to start, and it unmutes.