That seems like a bug in the drop-down...it should really present itself as a 'popup' or 'menu', so it doesn't interfere with other windows. Maximus would skip over it and it wouldn't show in the switcher, either.
For the short-term, you can add it's wm_class into /apps/maximus/exclude_class list. Grab thw wm_class using `xprop | grep WM_CLASS` and click on the volume-control window.
That seems like a bug in the drop-down...it should really present itself as a 'popup' or 'menu', so it doesn't interfere with other windows. Maximus would skip over it and it wouldn't show in the switcher, either.
For the short-term, you can add it's wm_class into /apps/maximus/ exclude_ class list. Grab thw wm_class using `xprop | grep WM_CLASS` and click on the volume-control window.