Comment 25 for bug 214370

> If the sound is playing in the background during shutdown, it'll get cut
> short because we save the mixer settings of the card and mute on the way
> down.
>
> If the sound is playing in the foreground, it'll make the shutdown take
> longer because we're waiting for the sound to finish playing.

I can tell you how it used to be, three releases ago: the sound would get cut short if it took too long (shutdown was the priority, correctly so, I think). There was a bit of art and skill involved in crafting a custom sound which would last just long enough to avoid this cruel fate. Personally, I'd like things back to this.

And yes, the bug is precisely that... It is listed as an option but doesn't function at all. Worst-case scenario is to remove the option; best-case is to make it work.