Hi, I think the problem is that you are using a Scrolled ROText widget, and therefore your $textbox is actually a scrolled widget, and will not respond to the -height option. I think you should test this with a plain ROText widget, and put the ROText widget into a scrolled pane to get the scrolling. Busy now, but I will try to see if I can get that idea to work. You can also try using the Subwidget method to get the real text widget.
my $realtextbox = $textbox->Subwidget('Scrolled');
and try to manipulate the $realtextbox's -height option.
If worse comes to worse, you could completely packForget the $mw, and rebuild it, but that would cause an annoying screen flicker, and necessitate
saving any text data, and reinserting it after the rebuild.