Previously all three of the Duration, PlaybackTime and Volume expressions would simply return a value for the first audio track with the given tag. That track could be a stopped track so this was actually working as intended, it would just be returning information for the first and stopped audio track when multiple tracks existed with the same tag. I think this demonstrates a valid use case for prioritising a playing track when deciding which track to return information for if there are multiple with the same tag. So I've changed this for the next build, hopefully that fixes it.