Well, the sample code I posted above does not seem to have this "one-time-only" limitation, so the question I posed there is still relevant. Are you sure your "re-configure" sub is being called when you expect it? Running Tk under the perl debugger can be very slow, but it might be worth a try -- put a breakpoint in the sub that resizes the listbox, and see whether the script always stops when you think it should. (And check variables while you're there, to make sure they contain what you expect.)