My take on it was it is hard to change the Label of stock image buttons, and most people wanted to be able to label their buttons as they desire. So it is turned off by default. Makes perfect sense to me.

With the way the Gtk2 themeing engine works, it is probable that it would be set in a ./gtkrc-2.0 theme setting.

#!/usr/bin/perl
use warnings;
use strict;
use Glib qw/TRUE FALSE/;
use Gtk2 '-init';

# create a new window
my $window = Gtk2::Window->new('toplevel');
$window ->signal_connect( "destroy" => sub { Gtk2->main_quit; } );


my $vbox = Gtk2::VBox->new( FALSE, 0 );
$window->add($vbox);
$vbox->set_border_width(2);

my $button = Gtk2::Button->new_from_stock('gtk-close');
my $button1 = Gtk2::Button->new_from_stock('gtk-close');
my $button2 = Gtk2::Button->new_from_stock('gtk-close');

$button->set_label('uh oh lost icon'); #won't work

# sub by muppet
find_and_set_label_in ($button2->child, "This worked");

$button->signal_connect( "clicked" => \&callback, "cool button" );
$button1->signal_connect( "clicked" => \&callback, "cool button1" );
$button2->signal_connect( "clicked" => \&callback, "cool button2" );

$vbox->pack_start( $button, FALSE, FALSE, 0 );
$vbox->pack_start( $button1, FALSE, FALSE, 0 );
$vbox->pack_start( $button2, FALSE, FALSE, 0 );

$window->show_all();

Gtk2->main;
##################################################
# our usual callback function
sub callback {
my $widget = shift;
my $data   = shift;

printf "Hello again - %s was pressed\n", $data;
}
##################################################

sub find_and_set_label_in {
 #muppet magic
 my ($widget, $text) = @_;
 print "@_\n";
 if ($widget->isa (Gtk2::Container::)) {
       $widget->foreach (sub { find_and_set_label_in ($_[0], $text); }
+);
    } elsif ($widget->isa (Gtk2::Label::)) {
       $widget->set_text ($text);
   }
}
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