POST json dictionary

I'm trying the following : A model with a dictionary inside send it on the first ajax request then take the result serialize it again and send it back to the controller.

This should test that I can get back a dictionary in my model. It doesn't work

Here's my simple test:

public class HomeController : Controller
{
    public ActionResult Index (T a)
    {
      return View();
    }

    public JsonResult A(T t)
    {
      if (t.Name.IsEmpty())
      {
        t = new T();
        t.Name = "myname";
        t.D = new Dictionary<string, string>();
        t.D.Add("a", "a");
        t.D.Add("b", "b");
        t.D.Add("c", "c");
      }
      return Json(t);
    }
}

//model
public class T
{
  public string Name { get; set; }
  public IDictionary<string,string> D { get; set; }
}

The javascript:

$(function () {
    var o = {
        Name: 'somename',
        "D": {
            "a": "b",
            "b": "c",
            "c": "d"
        }
    };

    $.ajax({
        url: actionUrl('/home/a'),
        contentType: 'application/json',
        type: 'POST',
        success: function (result) {
            $.ajax({
                url: actionUrl('/home/a'),
                data: JSON.stringify(result),
                contentType: 'application/json',
                type: 'POST',
                success: function (result) {
                }
            });
        }
    });
});

In firebug the json received and the json sent are identical. I can only assume something gets lost on the way.

Anyone has an idea as to what I'm doing wrong?

An unfortunate workaround:

data.dictionary = {
    'A': 'a',
    'B': 'b'
};

data.dictionary = JSON.stringify(data.dictionary);

. . .

postJson('/mvcDictionaryTest', data, function(r) {
    debugger;
}, function(a,b,c) {
    debugger;
});

postJSON js lib function (uses jQuery):

function postJson(url, data, success, error) {
    $.ajax({
        url: url,
        data: JSON.stringify(data),
        type: 'POST',
        contentType: 'application/json; charset=utf-8',
        dataType: 'json',
        success: success,
        error: error
    });
}

The ViewModel object being posted (presumably has a lot more going on than a dictionary):

public class TestViewModel
{
    . . .
    //public Dictionary<string, string> dictionary { get; set; }
    public string dictionary { get; set; }
    . . .
}

The Controller method being posted to:

[HttpPost]
public ActionResult Index(TestViewModel model)
{
    var ser = new System.Web.Script.Serialization.JavascriptSerializer();
    Dictionary<string, string> dictionary = ser.Deserialize<Dictionary<string, string>>(model.dictionary);

    // Do something with the dictionary
}

Due to the way JsonValueProviderFactory is implemented binding dictionaries is not supported.