Ok, it seems I jumped the gun. That Windows setting seemed to me the obvious culprit.
Since it doesn't seem to be that, maybe somebody else has a clue.
Still a bit strange that your level goes to exactly 80%, just like the aforementioned Windows sound setting.
I am not familiar with the Audio Switch and Audio Switcher software you mention and are using. Are you sure it is not some setting there?
- Is MusicBee lowering it's own volume, or some Windows volume slider?
- Do different player preferences settings (direct sound, wasapi etc.) make a difference?
- Does it also happen with MusicBee v3? It is still in a 'demo' phase, but if it is indeed a MusicBee issue, it's more likely to be addressed for v3, then for v2.
I'll move this topic back to Bugs again.