Really? Can you post the code? The following code does not work for me, I have to remove or die as shown in the commented line to make it work:

use strict;
use warnings;

use Tk;
use Tk::Listbox;

my $top = MainWindow->new;
my $f = $top->Frame->pack;
my $lb = $f->Listbox()->pack;

open my $STDIN,'-';
$top->fileevent($STDIN,
               readable =>
               sub {
                 chomp(my $line = <>);
                 # 
                 # $lb->insert('end',$line);
                 #
                 $lb->insert('end',$line) or die;
               });

MainLoop;
[download]