I need a bit of help with WidgetGrid usage in a custom publish event handler.

I have defined a property, panelPicker, as an xml stored WidgetGrid data type and would like to process the property value as part of a custom publish event handler. 

Have therefore defined an after publish event:

        void Document_AfterPublish(Document sender, umbraco.cms.businesslogic.PublishEventArgs e)
        {
            if (sender.ContentType.Alias == "landing") {
                NavigationManager.Instance.updateNavRelations(sender);
            }
        }

and a corresponding method to process the document:

        public void updateNavRelations(Document d)
        {
            if (d.ContentType.Alias == "landing")
            {
                Debug.WriteLine(d.getProperty("panelPicker").Value.ToString());
                XmlDocument xmlDoc = new XmlDocument();
                try
                {
                    xmlDoc.LoadXml(d.getProperty("panelPicker").Value.ToString());
                    Debug.WriteLine(xmlDoc.ToString());
                }
                catch (Exception ex)
                {                    
                    throw;
                }                
            }
        }

The property value is however returned as json despite the storage type being defined as xml. The database shows the property correctly stored as xml.

Any suggestions greatly appreciated.