Model CheckBoxFor Properties being posted twice Asp Net MVC 3

So I have a partial view...

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<NewsletterUnsubscribe_MVC3v2.Models.IntegraRecord>" %>

<% if (!String.IsNullOrEmpty(Model.ErrorMessage))
   {%>
   <div class="input-validation-error">
    <%:Model.ErrorMessage %>
   </div>
<% }
   else
   {%>

<% using (Html.BeginForm())
{%>
    <%:Html.ValidationSummary(true)%>
    <fieldset>
        <legend>IntegraRecord</legend>
        <div class="editor-field">
                <%:Html.LabelFor(m => m.EmailAddress)%>: <strong><%:Model.EmailAddress%></strong>
        </div>
        <%:Html.HiddenFor(m=>m.EmailAddress) %>
        <div class="editor-field">
                Unsubscribe from Area mailings: <%:Html.CheckBoxFor(m => m.AreaUnsubscribe)%>
        </div>
        <div class="editor-field">
                Unsubscribe from Monthly newsletters: <%:Html.CheckBoxFor(m => m.MonthlyUnsubscribe)%>
        </div>
        <p>
            <input type="submit" value="Save" />
        </p>
    </fieldset>
<% }
   }%>

When I hit submit and look what's in the posted data I see

EmailAddress:someone@somewhere.co.uk
AreaUnsubscribe:true
AreaUnsubscribe:false
MonthlyUnsubscribe:true
MonthlyUnsubscribe:false

As a result TryUpdateModel returns true but doesn't populate any fields

This gets posted to the controller...

 [HttpPost]
        public ActionResult GetRecord(IntegraRecord model)
        {
            if (TryUpdateModel(model))
            {
                try
                {
                    BusinessLayer.UpdateEmailAddress(model);
                }
                catch (ArgumentException)
                {
                    return View("Error", ViewBag.Message = "Could Not Update开发者_JAVA百科 Email Address.");
                }
            }
            return PartialView("GetRecord", model);
        }

Any help massively appreciated...

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Update: So following the clarification below (Thanks!)

I'm not using a custom model binder so I guess I'm missing some other convention too...

Here's my model...

public class IntegraRecord
    {
        private const string EmailRegex = @"[snip]";

        [Required(ErrorMessage = "Email Address is required")]
        [RegularExpression(EmailRegex, ErrorMessage = "This does not appear to be an email address")]
        public string EmailAddress;

        public bool AreaUnsubscribe;
        public bool MonthlyUnsubscribe;

        public string ErrorMessage;

        public IntegraRecord()
        {
        }

        public IntegraRecord(string email, bool area, bool monthly)
        {
            EmailAddress = email;
            AreaUnsubscribe = area;
            MonthlyUnsubscribe = monthly;
        }
    }

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That's how MVC handles checkboxes: asp.net mvc: why is Html.CheckBox generating an additional hidden input (and many other places) The problem is onthe server side (default model binder is aware of that and doesn't have a problem). Are you using custom model binder?