The "Mixer" window is much too easy to (!)-up with the mouse wheel!
So, you open up the "Mixer" window and there are lots of instruments there, so without thinking about it too much you move the mouse-wheel and ... whups! ... you just (irrevocably) changed a setting on some instrument. Unless you were paying attention (which you weren’t), you now have to try to guess what the setting was.
I suggest that this window (and other windows like them) should consist of information-display panels that are devoid of controls. To actually change an instrument, you double-click on it, which opens a modal dialog (with “OK” and “Cancel.”)
Thus, the act of changing a mixer setting becomes an explicit act, and it has the ability to Cancel.
The mouse-wheel should scroll up and down among these panels.