The follwing works as expected for me:

use strict;
use warnings;
use Tk;

my $mw = MainWindow->new (-title => "Place demo");

$mw->Label (-text=> 'Some sample text')->place (-x=>0, -y=>0);

MainLoop ();
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Perhaps you need to show a little more code. Something about as long at the sample that shows the probelm would be good.