In MatchEntryMListbox.pm, you have:

    my $scrolled_mlistbox = $popup_frame->Scrolled(
        qw/MListbox -selectmode browse -scrollbars oe/
        );
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Change scrollbars setting from oe to e, your GUI looked fine. I understand that oe is a valid setting, but...

    my $scrolled_mlistbox = $popup_frame->Scrolled(
        qw/MListbox -selectmode browse -scrollbars e/
        );
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But this is not a bug with Tk::MListbox, as this works:

use Tk;
use Tk::MListbox;

my $mw = MainWindow->new();
$ml=$mw->Scrolled("MListbox", -scrollbars=>"oe", -columns=>[[-text=>'H
+eading1', -sortable=>0], [-text=>'Heading2']])->pack();

MainLoop;
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