Why do I need to click the button twice for submitting when using Ajax Panel?
<telerik:RadAjaxPanel ID="RadAjaxPanel4" runat="server">
  <div class="customButton">
    <asp:LinkButton ID="lbtnSave" OnClientClick="return Page_ClientValidate();" 
                    runat="server" OnClick="lbtnSave_Click" CausesValidation="true">
      <img src="../admin/images/icons/16x16/save.png" /> 
      Save 
    </asp:LinkButton>
  <div class="customButton">
</telerik:RadAjaxPanel>