Nested Master Pages in ASP.NET results in missing controls!

I have the following Hierarchy:

MainMasterPage:

<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="MainAdmin.master.cs" Inherits="MyWebsite.Admin.MainAdmin" %><form id="form1" runat="server"><div id="MainMenu_Div" runat="server"><asp:ContentPlaceHolder ID="MainMenu" runat="server"/></div><div id="ContentArea_Div" runat="server"><asp:ContentPlaceHolder ID="ContentArea" runat="server"/></div></form>

TemplateMasterPage:

<%@ Master Language="C#" MasterPageFile="~/Admin/MasterPages/MainAdmin.Master" AutoEventWireup="true" CodeBehind="TemplateMasterPage.master.cs" Inherits="MyWebsite.Admin.TemplateMasterPage" %><asp:Content ID="ContentArea" ContentPlaceHolderID="ContentArea" runat="server"><div id="InputControls_Div" runat="server"><asp:ContentPlaceHolder ID="InputControls" runat="server" /><br /><asp:Button ID="Submit_Btn" runat="server" Text="Submit"            onclick="Submit_Btn_Click" /></div><div id="AfterSubmission_Div" runat="server" visible="False"><asp:Button ID="AnotherBtn" runat="server" CssClass="linkLookingButton"        onclick="AnotherBtn_Click" /></div></asp:Content>

TemplateMasterPage (Code Behind)

public partial class TemplateMasterPage : System.Web.UI.MasterPage{    public string BtnText    {        get { return AnotherBtn.Text; } //AnotherBtndoesn't exist in the current context        set { AnotherBtn.Text = value; } //AnotherBtndoesn't exist in the current context    }    protected void Page_Load(object sender, EventArgs e)    {    }    protected void Submit_Btn_Click(object sender, EventArgs e)    {        Submit_Btn.Enabled = false; //Submit_Btn doesn't exist in the current context        InputControls_Div.Visible = false; //InputControls_Div doesn't exist in the current context        AfterSubmission_Div.Visible = true; //AfterSubmission_Div doesn't exist in the current context    }

I commented the errors in my Code Behind sample .. this is used to work before using Nested Master Pages!