Hi Alrep,
You can wrap the navigation component along with the asp:ContentPlaceHolder within a UpdatePanel, e.g
<asp:UpdatePanel runat="server" ID="up1">
<ContentTemplate>
<telerik:RadNavigation ID="radNav" Skin="MetroTouch" Font-Size="Medium" runat="server" RenderMode="Auto">
<Nodes>
<telerik:NavigationNode Text="Test">
<Nodes>
<telerik:NavigationNode NavigateUrl="test1.aspx" Text="Test 1"></telerik:NavigationNode>
<telerik:NavigationNode NavigateUrl="test1.aspx" Text="Test 2"></telerik:NavigationNode>
</Nodes>
</telerik:NavigationNode>
</Nodes>
</telerik:RadNavigation>
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</ContentTemplate>
</asp:UpdatePanel>
For your convenience I have attached my test files.
If your scenario is different please modify them so that they start to exhibit the issue and send them back for examination.
Regards,
Rumen
Progress Telerik
Workaround: Include the Navigation in the partial postback response. E.g. Adding the Navigation as an AjaxUpdatedControl or putting the Navigation in an asp:UpdatePanel