Can't get ASP.NET 4 Web API to return Status Code "201 - Created" for successful POST

I am trying to return an HTTP Status Code of 201 Created for a RESTful POST operation using ASP.NET 4 Web API, but I always get a 200 OK.

I'm currently debugging on IIS 7.5.7600.16385, VS 2010 Professional, Windows 7 64-bit Professional.

public MyResource Post(MyResource myResource)
{
    MyResource createdResource;
    ...
    HttpResponse response = HttpContext.Current.Response;
    response.ClearHeaders(); // added this later, no luck
    response.ClearContent(); // added this later, no luck
    response.StatusCode = (int)HttpStatusCode.Created;
    SetCrossOriginHeaders(response);
    return createdResource;
}

I have seen other examples where HttpContext.Current.Response.StatusCode is set before returning data, so I didn't think this would be a problem. I haven't tracked it down in the MVC 4 source yet.

(This is related to my investigations with this question but different enough topic to warrant its own question)

I am not sure whether the problem is IIS or the Web API. I will do further tests to narrow it down.