In this case, the culture of the application is different from the culture of the machine. In this particular case, both cultures have different long date time format strings. current format mm/dd/yyyy compare to the one which the control is loading dd/mm/yyyy.

As a workaround, we can apply InvariantCulture before loading the XML and return the previous one after this:

CultureInfo.CurrentCulture = CultureInfo.InvariantCulture;
grid.LoadLayout(xml);
CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo("en-US");