jQuery .hide() doesn't work in some browsers

We are using jQuery .hide() to hide options in select inputs - when there are less than 31 days in a month. It works fine with Google Chrome and FireFox, but it doesn't work in Internet Explorer, Opera and Safari. Here is the JavaScript code we are using:

$(function() {
    // Show and hide days according to the selected year and month.
    function show_and_hide_days(fp_form) {
        var select_year= $(fp_form).find("select.value_year");
        var select_month= $(fp_form).find("select.value_month");
        var select_day= $(fp_form).find("select.value_day");
        var selected_year= parseInt($(select_year).val());
        var selected_month= parseInt($(select_month).val());
        var selected_day= parseInt($(select_day).val());
        var days_in_month= new Date(selected_year, selected_month, 0).getDate();
        if ((days_in_month >= 28))
        {
            // If selected day is bigger than the number of days in the selected month, reduce it to the maximal day in this month.
            if (selected_day > days_in_month)
            {
                $(select_day).val(days_in_month);
            }
            // Show all the days in this month and hide days which are not in this month.
            $(select_day).find("option").each(function() {
                var day= parseInt($(this).val());
                if (day <= days_in_month)
                {
                    $(this).show();
                }
                else
                {
                    $(this).hide();
                }
            });
        }
    }

    // Show and hide all days in this page.
    function show_and_hide_all_days() {
        $("select.value_day").each(function() {
            var form= $(this).closest("form");
            // Show and hide days according to the selected year and month.
            show_and_hide_days(form);
        });
    }

    // Show and hide all days in this page.
    show_and_hide_all_days();

    $("select.va