I can't duplicate your problem.

You're not changing @data, so (tied @data)->defer; and (tied @data)->flush; are useless. So is Tie::File, for that matter.

#!/usr/bin/perl

use strict;
use warnings;

$ENV{HOME} = 'C:\Documents and Settings\kompeS\Desktop\PERL SCRIPTS';
my $file = "$ENV{HOME}/partno_C7_5.03.4_prod";

open(my $fh, '<', $file)
   or die("Unable to open input file \"$file\": $!\n");

while (<$fh>) {
    my ($map_dir,$dir,$part_no,$chg_lvl,$int_lock,$t_spec) = split /\s
++/;
    print "    $map_dir,$dir,$part_no,$chg_lvl,$int_lock,$t_spec";
}
[download]