There seems to be an interaction between the Frame and the Checkbuttons. If you pack your Checkbuttons in the $mw, the -anchor=>'w' holds position, on a window resize. But if you add a Frame, and put the Checkbuttons in that Frame, the -anchor=>'w' dosn't hold the Checkbuttons, unless the Frame is packed with (-expand=>1, -fill=>'both').

Try resizing the $mw in this script with and without the Frame->pack(-expand=>1, -fill=>'both')

#!/usr/bin/perl
use Tk;
use strict;
use warnings;

# Main Window
my $mw = new MainWindow;

#GUI Building Area
my @style_sizes_array = qw(XXS XS S M L XL XXL XXXL);

# Checkbuttons won't hold left this way
#my $buttonFrame = $mw->Frame()->pack();

# works
my $buttonFrame = $mw->Frame()->pack(-expand=>1, -fill=>'both');

    #checkbutton sizes setup
    for (my $ctr = 0; $ctr < @style_sizes_array; $ctr++){
        my $size_type = $style_sizes_array[$ctr];

        $buttonFrame ->Checkbutton(-text => $size_type, -padx=>20, 
                          -variable => \$ctr)->pack(-anchor=>'w');
    }

MainLoop();
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