Parts of the sound system treat entry 0 as "no sound" so nothing placed there would play.
This made the one custom sound in "The Way of Ira" not play because as the last sound being defined it ended up in the first, invalid slot.
0 means 'default', -1 means 'silent'. This caused playback issues for useSoundGen. All other places were passing proper volume values along, this is the only one to read the volume from map data.