I believe I answered this a while ago. There is only one graphic for both track types, which can cause confusion when one doesn't read the help files. The confusion
could be reduced by creating a different graphic for MIDI tracks, but for all we know that might not be so easy. It might involve more research and development to implement.
The other point of confusion is that the "Gain" isn't really gain anyway - as one might expect on a real mixer. It's more of a pre-mix fader. The real gain is controlled by your interface/sound source output.
OAN, The "Master" vs. "Mains" label for the output tracks
would be an easy fix.