Hehe no that do not help :

$.fn.addItems = function (data) {
    return this.clearSelect().each(function () {
        if (this.tagName == 'SELECT') {
            var dropdownList = this;
            $.each(data, function (index, optionData) {
                var option = new Option(optionData.Text,
                         optionData.Value);
                if ($.browser.msie) {
                    dropdownList.add(option);
                }
                else {
                    dropdownList.add(option, null);
                }


                if ($(this).children().size() < 2) {
                    $(this).hide();
                }
                else {
                    $(this).show();
                }
            });
        }
    });
}

Now I get : elem.ownerDocument is undefined ( var defaultView = elem.ownerDocument.defaultView;)

I have checked that the $(this).children().size() returns the proper option count.