[Solved] Panel Bar Binding to SiteMap does not work

[Frank Michael]

I have this site map:

<?xml version="1.0" encoding="utf-8" ?>
<siteMap>
    <siteMapNode title="Home">
        <siteMapNode title="Workstream">
            <siteMapNode controller="Workitem" action="Index" title="Workitems" />
            <siteMapNode controller="Sprint" action="Index" title="Sprints" />
            <siteMapNode controller="Chart" action="BurndownChicDiagram" title="Burndown Diagram" />
        </siteMapNode>
        <siteMapNode title="Financial">
            <siteMapNode controller="Payment" action="Index" title="Payments" />
            <siteMapNode controller="RegularPayment" action="Index" title="Regular Payments" />
            <siteMapNode controller="Transaction" action="Index" title="Transactions" />
            <siteMapNode controller="Statement"  action="Index" title="Statement" />
            <siteMapNode controller="MinMax"  action="Index" title="Minimum Maximum Overview" />
            <siteMapNode controller="Chart" action="StatementChicDiagram" title="Statement Diagram" />
            <siteMapNode controller="Chart" action="MinMaxChicDiagram" title="Minimum Maximum Diagram" />
        </siteMapNode>
    </siteMapNode>
</siteMap>

and this page:

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %>
<%@ Import Namespace="Telerik.Web.Mvc" %>
<%

    if (ViewData["WorkstreamPlatform_WebRole.Menu"] != null)
    {
        Html.Telerik().PanelBar()
            .Name("navigation-product-examples")
            .HtmlAttributes(new { @class = "demos-navigation" })
            .BindTo("WorkstreamPlatform_WebRole.Menu")
            .HighlightPath(true)
            .ItemAction(item =>
            {
                if (!item.Items.Any() && !string.IsNullOrEmpty(Request.QueryString["theme"]))
                {
                    item.RouteValues.Add("theme", Request.QueryString["theme"]);
                }

                if (item.Selected)
                {
                    item.HtmlAttributes["class"] = "active-page";
                }

                if (item.Parent == null)
                {
                    item.SpriteCssClasses = "t" + item.Text;
                }
            })
            .Render();
    }

%>

and this Controller Action:

        [PopulateSiteMap(SiteMapName = "sample", ViewDataKey = "WorkstreamPlatform_WebRole.Menu")]
        public ActionResult Index()
        {
            ViewData["Message"] = "Welcome to ASP.NET MVC!";

            if (!SiteMapManager.SiteMaps.ContainsKey("sample"))
            {
                SiteMapManager.SiteMaps.Register<XmlSiteMap>("sample", sitmap => sitmap.LoadFrom("~/Web.sitemap"));
            }

            return View();
        }

It is very close to the sample, but does not work. The first level items are shown, but the second level items not.
Previously I had a situation where the first first level item (Workstream) did not expand, but the second (Financial) did expand. But since then I have made some changes, and I do not know the exact condition. So the current symptom is, that the first level items do not expand.
What bothers me as well I do not understand the general flow of the samle code.
In the sample there is an action:

public partial class MenuController : Controller
    {
        [PopulateSiteMap(SiteMapName = "sample", ViewDataKey = "sample")]
        [SourceCodeFile("Sitemap", "~/sample.sitemap")]
        public ActionResult SiteMapBinding()
        {
            if (!SiteMapManager.SiteMaps.ContainsKey("sample"))
            {
                SiteMapManager.SiteMaps.Register<XmlSiteMap>("sample", sitmap => sitmap.LoadFrom("~/sample.sitemap"));
            }

            return View();
        }
    }

It is not in the Home Controller
It is not clear to me when in the general flow this action is called. It seems to me that this is a callback from the client, but I am not sure. With my project, the action is never called. What can I do to understand the general flow? Is there an overview chart for this?
By the way: What does [SourceCodeFile...] mean? What is it for?

[Frank Michael]

This is the html

<li class="t-item t-state-default"><a class="t-link t-header" href="#"><span class="t-sprite tWorkstream"></span>Workstream<span class="t-icon t-arrow-down"></span></a></li><li class="t-item t-state-default"><a class="t-link t-header" href="#"><span class="t-sprite tFinancial"></span>Financial<span class="t-icon t-arrow-down"></span></a></li>