2 recently installed HomePods continue to play music (from separate sources) when all computers, iDevices have been shutdown, or so I believe. All devices on LAN are Apple - Macs/iPhone/iPad. Music seems to be from my local Apple sources - which may be iTunes? Power cycling HomePods no help. Both HomePods controlled from local iPhone 8S/iOS 11.4.
Ah sweet mysteries - whence forth cometh the music?