Homebridge/HA sends media_stop when I ask for turn off

Hi. I want to turn off my media player, but Siri/Homebridge stops it instead.
I have a media_player called Yamaha Zone 2.
When I ask Siri, “turn off Yamaha Zone 2”, I get this in my HA log:
<Event call_service[L] service_data=entity_id=media_player.yamaha_zone_2, service_call_id=1976154192-3182, service=media_stop, domain=media_player>

In my Homebridge log, I get:
homebridge[16965]: [2018-3-24 12:45:52] [HomeAssistant] Successfully set power state on the 'Yamaha Zone 2' to off

I note that this functionality used to work as expected, then changed.
Is this a bug, or is there a way I can change it?