Problem with Gtk2::Combobox->new_with_model

[Mike Martin <redtux1 gmail com>]

Hi - getting confused

I have a liststore
my $dvd_modelx=Gtk2::ListStore->new('Glib::String');
   foreach my $list (keys %cds){
         my $iter=$dvd_modelx->append();
        $dvd_modelx->set($iter, 0,$list )
        }

my $wid=Gtk2::ComboBox->new_with_model($dvd_modelx);# fails to add to combobox
my $wid=Gtk2::ComboBoxEntry->new_with_model($dvd_modelx);# succeeds in
 add to combobox

What am i missing here