What you are seeing is the group fader adjusting to the channel level that is the highest in the group. No need to worry about that. We do that to show the maximum possible level change. The other channels in the group do not change their level. A conventional DCA group does not show the relative levels so you can end up having a channel fader at the maximum and the group fader in the middle, for example. When you try to bring up the group fader nothing happens because the channel fader was at the maximum already. The M20d group fader just shows the level of the channel with the highest level so you know how much headroom there is. When you change the group level it behaves like a DCA group. All member channel levels change. When you change the level of a channel just that channel changes.