Including ASP.net Identity LoginPartial In Menu - Users not being signed in

Question

Within a navbar menu, I'm creating a dropdown menu that contains the LoginPartial.

Here's the LoginPartial code:

<li class="nav-item dropdown">
    <a href="#" id="LoginDropdownLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" role="button" class="nav-link dropdown-toggle fa fa-user-circle"></a>
    <div class="dropdown-menu" aria-labelledby="LoginDropdownLink">
        @using (Html.BeginForm("Login", "Account", new { ReturnUrl = "../../Home/Account" }, FormMethod.Post, new { @class = "form-horizontal", role = "form" }))
        {
            @Html.AntiForgeryToken()


            @Html.ValidationSummary(true, "", new { @class = "text-danger" })



            @Html.TextBoxFor(m => m.Email, new { @class = "input-text", @placeholder = "Email Address" })
            @Html.ValidationMessageFor(m => m.Email, "", new { @class = "text-danger" })



            @Html.PasswordFor(m => m.Password, new { @class = "input-text", @placeholder = "Password" })
            @Html.ValidationMessageFor(m => m.Password, "", new { @class = "text-danger" })


        @Html.CheckBoxFor(m => m.RememberMe)
        @Html.LabelFor(m => m.RememberMe)


        <input type="submit" value="Log in" class="btn btn-default" />


    }
</div>

And here's how I'm including it:

  <ul class="nav navbar-nav navbar-right">
                    <li><a class="active" href="../../Home/Index">Home</a></li>
                    <li><a href="../../Home/Build">Build A Box</a></li>
                    <li><a href="#ContactUs">Contact Us</a></li>
                    @Html.Action("LoginPartial", "Account")
                </ul>

Here's the controller code:

[HttpPost]
        [AllowAnonymous]
        [ValidateAntiForgeryToken]
        public async Task<ActionResult> Login(LoginViewModel model, string returnUrl)
        {
            if (!ModelState.IsValid)
            {
                return View(model);
            }


            // This doesn't count login failures towards account lockout
            // To enable password failures to trigger account lockout, change to shouldLockout: true
            var result = await SignInManager.PasswordSignInAsync(model.Email, model.Password, model.RememberMe, shouldLockout: false);
            switch (result)
            {
                case SignInStatus.Success:
                    if (model.OrderId != null)
                    {
                        Orders order = db.Orders.Where(x => x.OrderId == model.OrderId).First();
                        order.UserId = User.Identity.GetUserId();
                        db.SaveChanges();
                        return RedirectToAction("Checkout1", "Home", new { model.OrderId });
                    }
                    else
                    {
                        return RedirectToAction("Index", "Account");
                    }

                case SignInStatus.LockedOut:
                    return View("Lockout");
                case SignInStatus.RequiresVerification:
                    return RedirectToAction("SendCode", new { ReturnUrl = returnUrl, RememberMe = model.RememberMe });
                case SignInStatus.Failure:
                default:
                    ModelState.AddModelError("", "Invalid login attempt.");
                    return View(model);
            }
        }

I put a breakpoint on the var result=... line, and found that the result is "Success." However, rather than loading the Account/Index page, I get redirected to the login page (with the return URL):

http://localhost:51511/Account/Login?ReturnUrl=%2FAccount

I'm including the Account/Index controller code for completeness. I added an [AllowAnonymous] attribute to it temporarily to see what would happen, and it did load (but the model contained no data, of course).

public ActionResult Index()
{
    AccountIndexViewModel model = new AccountIndexViewModel();
    var Current = User.Identity.GetUserId();
    model.Orders = db.Orders.Where(x => x.UserId == Current).OrderByDescending(x=> x.Date).ToList();
    List<string> OrderIds = db.Orders.Where(x => x.UserId == Current).Select(x => x.OrderId).ToList();
    model.OrderDetails = db.OrderDetail.Where(x=> OrderIds.Contains(x.OrderId)).ToList();
    return View(model);
}