Filed a bug with Apple 6 months ago. Haven't heard anything and the bug is still there.

How to reproduce the bug on iPhone/iPad:

- start playing some music

- open control center and swipe down on the volume to mute it

- turn up the volume one click on the physical buttons

- swipe down on the volume in control center

- repeat turning up the volume with the buttons and muting in the control center until the control center volume stops affecting the actual volume