In general this is the expected behavior when you set NavigateUrl
property of the control. However, if you need the tab not to look selected you could get the correct css class selector and override the existing styles. You can take a look at the following help topic
where the different css classes are fully described.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed