Following my post & a mail to harlequin CLIM support I received an answer to
my question about how to make list-panes update & refresh from Harlequin
CLIM support. Here's the process :
Items may be added to a list pane using clim:set-gadget-items as a place
indicator. i.e. (push 'new-item (set-gadget-items my-pane))
A gadget is refreshed using the sheet protocol. Repaint sheet works for me.
(repaint-sheet my-pane (sheet-region my-pane))
Many thanks to Harlequin's CLIM support.