Hi Daniel (and Lucien, who replied privately):
(1) thanks for the "not dumb" comment.
Sorry additionally for not being clear. The app is intended for the buttons (will eventually be checkboxes, but buttons were simpler for purposes of isolating the behavior) to be dynamic (unknown at layout time as things to be checked will come and go during program execution).
So while I did have some joy with making :list-panes with :items in the definition of the application frame (and it was prettier than what I sent), I had less joy changing those items programmatically.
When I put a "terpri" in as in the slightly revised test program as the other alternative, I get a blank line between the gadgets, which (given I am going to have a lot of items) would cause the user excess scrolling due to the whitespace between boxes.
-jm