Following along with the book the example does not work for me. I found that I needed to add
this.TestPanel.Language = XmlLanguage.GetLanguage(Thread.CurrentThread.CurrentCulture.Name);
The problem is that DateTime values are not parsed correctly if your culture uses anything apart from m/d/yyyy. I think that the example would have worked for me if I ran it on 5/5/2012 or 6/6/2012 or anything where the month and day were the same.