So what is a bit strange and I don't know if this is by design or not
is that all mute & solo buttons send the same controller CC as the volume fader.
(by default: CC7. if the volume slider is assigned to a different CC, then they also send a different CC)
They do this in a toggled fashion: 0 & 127. You press one solo or mute button and the CC7 is send on ALL ports/channels,
which messes up everything that is connected to the ports and responds to the CC number in question(!)
If this is NOT by design, it would be good to disable this, as using the Volume CC7 from the mixer to control
external synths/host/etc volume - is very nice. However, as soon as I press mute or solo, everything (!)
on all outputs/ports/channels that respond to CC7 gets messed up.
Best,
tL.