The cause of your output is beyond me; however, I'd suggest a different approach to aquiring the numbers:

#! /usr/bin/perl

use strict ;
use warnings ;
# $|++ ;

while ( <DATA> )
{
    /^Phys.*(\w)-(\w\w)-(\w\w)$/ ;
    my $match = 'hhh' . $1 . $2 . $3 . 'kk' ;
    print "The new string is: $match\n" ;
    last ;
}

__DATA__
Physical Address. . . . . . . . . : 00-B0-D0-87-52-19
DHCP Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : 192.45.10.166
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_______________
DamnDirtyApe

Those who know that they are profound strive for clarity. Those who
would like to seem profound to the crowd strive for obscurity.
            --Friedrich Nietzsche