Just do:

| finder |  
    finder := GLMFinder new.
    finder with: [:f |
        f
            showFirst: [:a | a list]; 
            show: [:a | a list display: [:x | 1 to: x]
            ]].
    finder openOn: (1 to: 42).

And you will notice that as you scroll, the space between the finder panes is white
instead of transparent.