Solved it.

my @mpy = ();
my @mpe = ();
my @mpya = ();
my @mpea = ();
foreach my $drp ( 0 .. $LST ) {
    my $row = $drp + 2;
    $mpy[$drp] = $mw->Entry( -width => 5,-textvariable =>\$mpya[$drp] 
+)->pack();
    $mpy[$drp]->grid( -row => $row, -column => 1, -in => $table );
    $mpe[$drp] = $mw->Entry( -width => 5,-textvariable =>\$mpea[$drp])
+->pack();
    $mpe[$drp]->grid( -row => $row, -column => 2, -in => $table );
}
[download]

At least it prints to the MainWindow properly

Now, why this didn't work the first time I tried it, I have no idea.