UserControl Causes Full Postback In UpdatePanel

I'm having few UpdatePanels on my master page. And then, I have RadTreeViewcontrol on the page, that should cause partial postback each time node is clicked. Everything works fine there. Since I'm using the same tree on some other pages, I moved this functionality to UserControl. Stuff I've done before, so no problem. Moved some code to ascx, created some events. Everything always worked for me well. But not now. RadTreeView is nested inside UserControl, and this control on master page with update panels, see below:

<asp:Panel ID="pnlContentWrapper" runat="server" CssClass="ContentWrapper">
<div id="HeaderBreadCrumb">
<asp:ContentPlaceHolder ID="HeaderBreadCrumbContent" runat="server" />
</div>
<div id="HeaderMenu">
<asp:UpdatePanel ID="upnlTreeMenu" runat="server">
<ContentTemplate>
<asp:ContentPlaceHolder ID="HeaderMenuContent" runat="server" />
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="treeProductTree" />
</Triggers>
</asp:UpdatePanel>
</div>
<div id="TreeDiv">
<fp:ProductTree ID="treeProductTree" runat="server" />
</div>
<asp:Panel ID="ContentDiv" ClientIDMode="Static" runat="server">
<asp:UpdatePanel ID="upnlTreeContent" runat="server">
<ContentTemplate>
<asp:ContentPlaceHolder ID="TreePageContent" runat="server" />
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="treeProductTree" />
</Triggers>
</asp:UpdatePanel>
</asp:Panel>
</asp:Panel>
And the user control is really simple:
<%@ Control Language="vb" AutoEventWireup="false" CodeBehind="ProductTree.ascx.vb"
Inherits="ProductTree" %>
<div>
<telerik:RadTreeView ID="treeProductTree" ClientIDMode="Static" runat="server" EnableDragAndDrop="false"
SkinID="CustomSkin" CssClass="MasterProductTree" DataFieldID="NodeId" DataFieldParentID="NodeParentId"
DataTextField="NodeName" DataValueField="NodeId" />
</div>

And some code behind:

Imports Telerik.Web.UI
Public Class ProductTree
Inherits System.Web.UI.UserControl
Public Event NodeExpand As EventHandler(Of ProductTreeNodeExpandEventArgs)
Public Event SelectedNodeChange As EventHandler
Protected Sub ProductTree_NodeExpand(ByVal sender As Object, ByVal e As RadTreeNodeEventArgs) _
Handles treeProductTree.NodeExpand
Dim nodeId As Integer = CInt(e.Node.Value)
Dim evetArgs = New ProductTreeNodeExpandEventArgs(nodeId)
RaiseEvent NodeExpand(Me, evetArgs)
//'some logic
End Sub
Protected Sub ProductTree_OnNodeClick(ByVal sender As Object, ByVal e As RadTreeNodeEventArgs) _
Handles treeProductTree.NodeClick
RaiseEvent SelectedNodeChange(Me, New System.EventArgs())
End Sub
End Class

What I don't know is: why is this causing full postback instead of partial? I suspect that it may have something to do with raising my for SelectedNodeChange, but I don't know how to deal with it other way. I need to let other components know, that node selection changed. How can I improve this to make it work with UpdatePanels?