Hi jho, Whats happening here is that the surface controller dosent know what page you coming from and cant return "CurrentUmbracoPage" with the Html.ActionLink.

I would solve this using a RenderMvcController and pass in the sorting category to it and from the controller return a custom RenderModel to get rid of your TempData fields.

Create a RenderMvcController naming it: Document Type name = controller name Template name = action name and create a view model

public class HomeController : Umbraco.Web.Mvc.RenderMvcController
{
    public ActionResult HomePage(RenderModel model, int sort)
    {
        var viewModel = new HomePageViewModel(model.Content)
                            {
                                Sort = sort
                            };

        return base.Index(viewModel);
    }
}


public class HomePageViewModel : RenderModel
{
    public HomePageViewModel(IPublishedContent content)
        : base(content)
    {
    }

    public int Sort { get; set; }
}

Then you can use a Html.Action to render your partial. Like this:

@Html.Action("SortBy","AssignmentSurface", new { nodeId = Model.Content.Id, sortCategory = Model.Sort })

And finally in your Surface controller return the partialview:

public class AssignmentSurfaceController : SurfaceController
{
        [AcceptVerbs(HttpVerbs.Get)]
        public ActionResult SortBy(int nodeId, SortCategory sortCategory)
        {
            var overviewPage = DocumentTypeHelper.GetDocument<AssignmentOverviewPage>(nodeId);
            var assignmentViewModel = new AssignmentViewModel(overviewPage);
            var assignments = new AssignmentManager().GetAll();

            switch (sortCategory)
            {
                case SortCategory.ID:
                    assignments = assignments.OrderBy(x => x.ID);
                    break;
                default:
                    return null;
            }

            assignmentViewModel.AllAssignments = assignments.ToList();
            TempData["viewModel"] = assignmentViewModel;

            return PartialView("ListAllAssignments", assignmentViewModel);
        }
}

Your sorting urls would now look like this:

<a href="@(Model.Content.Url + "?sort=" + 123)">Sort</a>

Good luck!