Currently the SiteMap.CurrentNode
property is implemented to return the current node if it is navigable or the first navigable parent node. Perhaps, in your case it returns null, because there is no navigable parent.
But it seems that this is not the most appropriate behavior of the SiteMapProvider, so we decided to make a few changes for the upcoming service pack. The SiteMap provider should always contain all pages. Also, the navigable controls should return only navigable pages and the SiteMap.CurrentNode
property should return the current page node no matter if it is set as navigable or not.
We think that these improvements will cover more scenarios.
All the best,
the Telerik team