A Scrolled object is not the real thing, it's the parent of the real thing. Mostly, things work properly, but not always.

Get the real canvas and apply ->scale to that:

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1146938

use strict;
use warnings;
use Tk;


sub GUI() {
    my $fenetre  = new MainWindow(
  -title      => 'test',
  );
    $fenetre->minsize( 200, 70 );


    my $cadre_voie = $fenetre->Frame()->pack(-fill => 'both', -expand 
+=> 1);
    my $voie = $cadre_voie->Scrolled(
  'Canvas',
  -background  => '#A0A0A0',
  );
    $voie->pack(-fill => 'both', -expand => 1);
    my $realcanvas = $voie->{SubWidget}{canvas};

    $cadre_voie->Scale(-orient=>'horizontal')-> pack();
    #$fenetre->repeat( 500, sub { $voie->scale('all',0,0,1,1); } );
    $fenetre->repeat( 500, sub { $realcanvas->scale('all',0,0,1,1); } 
+);
    MainLoop;    # Obligatoire
}

GUI();
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