When changing output routing, you can press shift option and then click to assigning output for multiple selected channels.
This works when clicking the desired output in the list with a mouse, but if you select and hit enter with the keyboard only the first channel is assigned.
Perhaps a better approach would be to just assign output of all selected channels regardless of keyboard modifiers.
Just noticed it as well, very annoying.
All-though with routing I find it less troublesome, as I would use the mouse anyway, but changing the gain setting on multiple channels, using Enter on the keyboard would be more “logical”, now I’m going back and forth from mouse to keybaord and back…