strange refresh of a "docked" listbox

[autocart]

Hi,
I have this scenario:
I have a listbox inside a palette (or control bar - same behaviour). When the form is docked then either the selchanged event of the listbox or the "vla-activate <document>" function (which is called inside the event) seems to trigger a refresh or rebuild of the listbox. When I have more than 2 or 3 items in the listbox (i.e. maybe 15) then this causes a delay of about 1 second (the more items the longer delay).
BUT ... when the form is floating (not docked) then there is no visible refresh (causing a delay).

Does anybody have a solution or a workaround?
Thx and regards, Stephan