Culture specific DateTime string is inconsistent between platforms

Question

I have a test application that allows the user to select a culture from a ComboBox and displays the culture specific date in a multiline TextBox. The code is below:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        comboBox1.Items.AddRange(
            CultureInfo.GetCultures(CultureTypes.SpecificCultures));
    }

    private void comboBox1_SelectedValueChanged(object sender, EventArgs e)
    {
        CultureInfo selectedCulture = comboBox1.SelectedItem as CultureInfo;
        DateTime currentDate = DateTime.Now;

        textBox1.Text =
            "My Date : " + currentDate.ToString() + Environment.NewLine +
            "Culture Specific Date: " + currentDate.ToString(selectedCulture);
    }
}

I notice that if "ar-SA", Arabic (Saudi Arabia), is selected, then I see different results when I run the application on different machines.

On a Windows 7 machine, the text box displays:

My Date : 4/11/2012 4:07:09 PM
Culture Specific Date: 19/05/33 04:07:09 م

On a Windows XP machine, the text box displays:

My Date : 4/11/2012 4:07:09 PM
Culture Specific Date: 20/05/33 04:07:09 م

As you can see, the culture specific date is off by a day. What could be causing this discrepancy?

Answer 1

I suspect this is due to the Windows XP machine not receiving up-to-date adjustments to the Umm al-Qura calendar, whereas presumably the Windows 7 box is kept up to date, although I wouldn't expect those adjustments to affect the current month. Alternatively, it could be due to this:

Only recently has more information become available which now makes it possible to reconstruct the calendar adopted on the Arabian Peninsula in the recent past and to predict its future course for many years in advance.

... so maybe the Windows XP implementation is out of date.

(That page agrees that it's currently the 19th, by the way.)