widget reuse

[Beast <beast i6x org>]

Just curious, why reuse widget is not works:

   my $spacer = Gtk2::Label->new();
   $spacer->set_size_request(30,0);

   $hbox->pack_start($spacer,FALSE,FALSE,0);
   $hbox->pack_start($vbbox,FALSE,FALSE,0);
   $hbox->pack_start($spacer,FALSE,FALSE,0);

error:

Gtk-CRITICAL **: file gtktable.c: line 598 (gtk_table_attach): assertion 
`child->parent == NULL' failed at

TIA

--

--beast