ComboBox has a default value and it look like when this
gets updated the object gets reset.
Look at lines 50 to 56 that I changed and it is working.

#!/usr/bin/perl
use Tk;
use Tk::JComboBox;

my $screen_size = "1010x720+0+0";
my $tool_name='Testing Interface';

&Screen();
MainLoop;

#-------Drawing User interface screeen----------------------
sub Screen {
    $main_screen_object = MainWindow->new(-bg => 'white');
    $main_screen_object->geometry($screen_size);
    $main_screen_object->title($tool_name);
    createButton('CREATE NEW WINDOW',15,490,150,$main_screen_object);
}

#-------Callback function 'CREATE NEW WINDOW' button------------------
+------
sub onCREATENEWWINDOWButtonClick {
    $main_screen_object->update();    
    $CopyWindow=$main_screen_object->Toplevel(-height => 240, -width =
+> 270, -background => 'white', -title => 'Copy Mapping') or die "coul
+d not instant\n";
    createLabel('COUNTRY',30,25,undef,undef,undef,$CopyWindow);
    our @CountryCodesList=qw /HD NK ID LK/;
    createComboBox('CountryCodes',10,140,25,$CopyWindow);
}

sub onCountryCodeComboBoxSelect {
}

#-------createLabel() - Used to create the label widget for given conf
+iguration---------------
sub createLabel {
    my($LabelName,$x,$y,$background,$Font,$Foreground,$Object) = @_;
    $Font = 'verdana 10 bold' unless defined $Font;
    $background = 'white' unless defined $background;
    $Foreground = '#015F96' unless defined $Foreground;
    my($LabelNameObject);
    if ( defined($Object) ) {
        $LabelNameObject = $Object->Label(-background =>$background,-t
+ext =>$LabelName,-font =>$Font,-foreground =>$Foreground)->place(-x=>
+$x,-y=>$y);
    } else {
        $LabelNameObject = $main_screen_object->Label(-background =>$b
+ackground,-text =>$LabelName,-font =>$Font,-foreground =>$Foreground)
+->place(-x=>$x,-y=>$y);
    }
    return($LabelNameObject);
}

#-------createComboBox() - Used to create the combobox widget for give
+n configuration---------------
sub createComboBox {
    my($ComboBoxName,$Width,$x,$y,$Object) = @_;
    $ComboBoxName =~ s/\s+//g;
#---------------------------------------------------------    
#---------------------------------------------------------    
# the combobos list get update with the last select value 
# that is way I plased this line here and it is working
    my @combolist = @{$ComboBoxName."List"};
#---------------------------------------------------------    
#---------------------------------------------------------    
    
    my $ComboBoxObject = $Object->JComboBox(-background =>'white',
                  -textvariable => \${$ComboBoxName},
                  -choices => \@combolist,
                  -browsecmd =>\&{"on".$ComboBoxName."ComboBoxSelect"}
+,
                  -font =>'verdana 10',
                  -relief => 'solid',
                  -borderwidth => 1,
                  -entrywidth => $Width
                    )
                  ->place(-x=>$x,-y=>$y) or die "Error $! \n\n";
    return($ComboBoxObject);
}

#-------createButton() - Used to create the button widget for given co
+nfiguration---------------
sub createButton {
    my($ButtonLabel,$Width,$x,$y,$Object) = @_;
    my($ButtonObject);
    
    my $ButtonName = $ButtonLabel;
    $ButtonName =~ s/\s+//g;
    $ButtonObject = $Object->Button(-background =>'grey',
                                -text =>"$ButtonLabel",
                                -font =>'verdana 10 bold',
                                -foreground =>'black',
                                -disabledforeground => '#90938D',    
                                -activebackground=>'#4A71AD',
                                -activeforeground => 'white',
                                -relief => 'solid',
                                -borderwidth => 1,
                                -width =>$Width,
                                -command =>\&{"on".$ButtonName."Button
+Click"})->place(-x=>$x,-y=>$y);
    return($ButtonObject);
}
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