ReturnUrl Duplicating Parameters - MVC 4

I'm having problem with retunUrl what is duplicating my QueryString parameters.

My url is like:

"www.mysite.com/Order/?id=1&item=123"

then, redirect me to login page and the url look like:

"www.mysite.com/login/RedirectUrl=/Order?id=1&item=123&id=1&item=123"

After the user login, the action redirect to:

"www.mysite.com/Order/?id=1&item=123& id=1&item=123 "

In my page when i use Request.QueryString["id"] i got an error, because the querystring "ID" is duplicated.

My login Action code look like this:

[HttpPost]
[AllowAnonymous]
public ActionResult Index(LoginModel model, string ReturnUrl)
{
    if(VerifyLogin(model))
    {
       if(ReturnUrl != null)
          return Redirect(ReturnUrl);//redirect to url with duplicated parameters
       else
          return Redirect("/Home");
    }
    else
    {
       ModelState.AddModelError("", "Invalid Username or Password");
    }

   return View();
}

How i can solve this problem?