title: Model change in post action not visible in Html.TextBoxFor?
body: <p>This must be something very obvious but for me it looks very strange. I have simple controller, model with one property, and view which displays value of property and renders editor for that property. When I click the button, form is posted and exclamation mark is appened to property. This exclamation mark is visible in my view but only in <code>p</code> tag, not in <code>input</code> tag rendered by <code>Html.TextBoxFor()</code>.</p>
  
  <p>Why <code>Html.TextBoxFor()</code> ignores that I updated my model in post action?</p>
  
  <p>Is there any way to change this behavior of <code>Html.TextBoxFor()</code>?</p>
  
  <p>View</p>
  
  <pre><code>@model ModelChangeInPostActionNotVisible.Models.IndexModel
  
  @using (Html.BeginForm())
  {
      &lt;p&gt;@Model.MyProperty&lt;/p&gt;
      @Html.TextBoxFor(m =&gt; m.MyProperty)
      &lt;input type="submit" /&gt;
  }
  </code></pre>
  
  <p>Model</p>
  
  <pre><code>namespace ModelChangeInPostActionNotVisible.Models
  {
      public class IndexModel
      {
          public string MyProperty { get; set; }
      }
  }
  </code></pre>
  
  <p>Controller</p>
  
  <pre><code>namespace ModelChangeInPostActionNotVisible.Controllers
  {
      public class HomeController : Controller
      {
          public ActionResult Index()
          {
              return View(new IndexModel { MyProperty = "hi" });
          }
  
          [HttpPost]
          public ActionResult Index(IndexModel model)
          {
              model.MyProperty += "!";
              return View(model);
          }
      }
  }
  </code></pre>
  
  <p>HTML after clicking on submit button</p>
  
  <pre><code>&lt;form action="/" method="post"&gt;    &lt;p&gt;hi!&lt;/p&gt;
  &lt;input id="MyProperty" name="MyProperty" type="text" value="hi" /&gt;    &lt;input type="submit" /&gt;
  &lt;/form&gt;
  </code></pre>