Workaround: 
public class MyRadPivotGrid : RadPivotGrid
{
    public override void SaveLayout(string fileName)
    {
        ComponentXmlSerializer ser = new ComponentXmlSerializer(this.XmlSerializationInfo);

        using (XmlTextWriter writer = new XmlTextWriter(fileName, Encoding.UTF8))
        {
            writer.Formatting = Formatting.Indented;
            writer.WriteStartElement("RadPivotGrid");
            ser.WriteObjectElement(writer, this);
        }
    }
}