ASP.NET button changes page - Ends up out of div - asp.net

Question

The problem happens on this page. When you press Button 1 a table is displayed on the page. Pressing Button 2 does nothing at all (empty function), but for some reason the button ends up out of the div it is in.
I use twitter bootstrap CSSs (latest version - 2.2.1)
Here's the markup:
<%# Page Language="C#" AutoEventWireup="true" MasterPageFile="~/Site.master" CodeBehind="Test.aspx.cs" Inherits="CalendarImporterWeb.WebForm1" %>
<%# Register TagPrefix="uc" TagName="Timetable" Src="~/TimetableControl.ascx" %>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManagerMain" runat="server" />
<script language="javascript" type="text/javascript">
<!--
function popupWindow(url) {
newwindow = window.open(url, 'name', 'height=520,width=500');
if (window.focus) { newwindow.focus() }
return false;
}
function showControl(controlID) {
var control = document.getElementById(controlID);
control.style.display = "block";
control.style.visibility = "visible";
}
function hideControl(controlID) {
var control = document.getElementById(controlID);
control.style.display = "none";
}
// -->
</script>
<table border="0" width=500>
<tr height="50">
<td colspan="2" align="left">
<asp:Button runat="server" id="btnGetCourses" text="Button 1" CssClass="btn btn-info"
OnClientClick="showControl('ImageSpinner');" onclick="btnGetCourses_Click" />
</td></tr>
</table>
<br />
<asp:UpdatePanel ID="UpdatePanel1" runat="server" updatemode="Conditional">
<Triggers>
<asp:AsyncPostBackTrigger ControlID="btnGetCourses" EventName="Click" />
</Triggers>
<ContentTemplate>
<uc:Timetable id="Timetable1" runat="Server" Visible="false"></uc:Timetable>
</ContentTemplate>
</asp:UpdatePanel>
<div class="jumbotron">
<asp:button id="btnStart" class="btn btn-primary" runat="Server"
Text="Button 2" onclick="btnStart_Click" />
<br /><br />
</div>
</form>
</asp:Content>
And the cs:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace CalendarImporterWeb
{
public partial class WebForm1 : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void btnGetCourses_Click(object sender, EventArgs e)
{
Timetable1.LoadCourses("","","");
}
protected void btnStart_Click(object sender, EventArgs e)
{
}
}
}

Answer 1

It looks like you have an extraneous "-->" in your markup somewhere - I see it on the rendered page at the top right.

Answer 2

Found the problem:
The TimetableControl had a spare /div in its code. Since it was not visible (ASP.NET Visible property, not HTML visible property) it didn't matter until it was made visible
Thanks for the help