Don't usually have access to a Windows machine, but one was here so I gave your code a try with "strawberry-perl-5.20.1.1-32bit", and the same versions of ItemStyle and Tree as you. After adding a couple lines to the top, it worked without the problems you described:

use strict;
use warnings;
use Tk;
use Tk::Tree;
use Tk::ItemStyle;
[download]

Might be worth upgrading if that's an option. GL