I simplified the code a bit more by using Tkx::Scrolled, to see if anything changed. Since the Scrolled widget really uses the same stuff behind the scenes, I didn't expect anything different:

#!/usr/bin/perl -w

use strict;
use Tkx;
use Tkx::Scrolled;

my $mw = Tkx::widget->new(".");
my $lb = $mw->new_tkx_Scrolled("listbox", -scrollbars => "e", -height 
+=> 10);
$lb->insert("end", 1..100);
$lb->g_grid(-column => 0, -row => 0);

Tkx::MainLoop();
[download]

Basically, I can scroll up and down with the keyboard (arrow keys and page up/down) and the mouse (if I grab the scrollbar with the mouse and move it up and down). I can also scroll down if I roll the mouse wheel downwards, but I cannot scroll up by rolling the mouse wheel upwards.

I am tempted to bring up a Linux VM and seeing what this code does outside of Windows. However, that means bringing up a new VM, installing Tcl/Tk, and all the associated Tkx perl modules. So... maybe not tonight.