title: When I post back to my controller all values for my model are null
body: <p>I have cut the model back to one field:</p>
  
  <p>//Model</p>
  
  <pre><code>public class LetterViewModel
  {
      public string LetterText;
  }
  </code></pre>
  
  <p>//Controller</p>
  
  <pre><code>public ActionResult Index()
  {
      var model = new LetterViewModel();
      model.LetterText = "Anything";
  
      return View(model);
  }
  
  [HttpPost]
  public ActionResult Index(LetterViewModel model)
  { 
      //model.LetterText == null
      return View(model);
  }
  </code></pre>
  
  <p>//view</p>
  
  <pre><code>@model Test.Models.LetterViewModel
  @{
      Layout = "~/Views/Shared/_Layout.cshtml";
      ViewBag.Title = "Create a Letter";
  }
  @using (Html.BeginForm())
  {
      &lt;div id="Bottom"&gt;
          @Html.TextAreaFor(m =&gt; m.LetterText)
          &lt;input type="submit" value="Ok" class="btn btn-default" /&gt;
      &lt;/div&gt;
  }
  </code></pre>
  
  <p>When I check the Network tab in dev tools it is showing the value entered is being included in the request.  However, when the HttpPost controller is fired the field is empty.</p>