Doing some more work with magic sheets, I've uncovered what seems to be an inconstistancy, and a fustrating one.
If you choose a channel by clicking/touching, then set it to a level via keypad, then choose another channel, the two channels get combined on the CLI. If I've set the channel to a level, the consistent thing to do would be to start a new channel selection when I choose a new channel. That is:
Click a light targetted to channel 1.
Type @ 20 <Enter>
Click a light targetted to channel 2.
CLI now reads 1+2 , it should read 2 Only.