I'm using an Android (Samsung S5). I have the official cover for the phone, so when you close the cover there is a little window and you can still control aspects of your phone.
So when I close it currently I can still use spotify, it comes up with the the image of the song being played. Pause, next and previous song. However the VOLUME button at the upper right of this applet controls the 'Media' volume, i.e. the volume on the phone, but I have Spotify 'Connected to a device', i.e. my Sonos speaker, so it really should adjust the volume of the speaker and not the phone volume, as this does nothing because there is no volume coming from the phone.
Any advice? I'm assuming this is a bug.