Ctrl-clicking on M and on P in the leadsheet window, I get treble clef for Melody plus treble and bass clef for Piano.

To display just treble clef for Melody and bass clef for Piano, try Edit "Copy/Move tracks ..." to copy the content of the piano track onto the melody track while keeping the content of the melody track.

Then displaying treble and bass clef of just the melody track should get you to second base.

Martin