Task.Factory.StartNew and blocking UI

I have tested your code in a WPF targeting NET Framework 4 project in VS 2015 update 4, and I do not know what you mean by "ticking" the UI, but what happens is that the user does not know that the search is over because no code is executed in the Continuation Action. So at the end of the search, everything continues the same and it seems that nothing has been done.

As you have coded it, the Continuation Action is executed in the thread of the UI when finishing the search, so there you can change the graphic elements, and at least you would have to show the found articles linking the collection Articles to a Graphic element such as a ListView or a GridView.

For example:

 private void Buscar()
    {

        ShowMessage = "Buscando...";

        IsBusy = true;

        ShowProgressRing = true;

        Task.Factory.StartNew(() =>
        {

            //Thread.Sleep(5000); // Simulate SQL query

            Articulos = new ObservableCollection<Articulo>();

            for (var i = 0; i < 500; i++)
            {
                Articulos.Add(new Articulo
                {
                    Codigo = i.ToString(),
                    NombreDelArticulo = "PRODUCT NAME",
                    PrecioFinal = 1m
                });
            }

            IsBusy = false;

        }).ContinueWith(x =>
        {

            MessageBox.Show("Búsqueda finalizada, pulse para ver los artículos encontrados");
            ArticulosLW.ItemsSource = Articulos;

        }, TaskScheduler.FromCurrentSynchronizationContext());

    }

What is happening to you, is that you are modifying within a task, an object that did not create that task, in this case the object Articles, which must be a property of the Window object.

This is fixed, creating a task that creates an object like the one you need (in this case, an ObservableCollection and when it finishes, it returns it and urges it to the one you need to feed in. With async / await, it's very simple.

Here is your modified example:

private async void Buscar()
{

    ShowMessage = "Buscando...";

    IsBusy = true;

    ShowProgressRing = true;

    Articulos = await Task<ObservableCollection<Articulo>>.Run(() =>
    {

        //Thread.Sleep(5000); // Simulate SQL query

        var newArticulos = new ObservableCollection<Articulo>();

        for (var i = 0; i < 500; i++)
        {
            Articulos.Add(new Articulo
            {
                Codigo = i.ToString(),
                NombreDelArticulo = "PRODUCT NAME",
                PrecioFinal = 1m
            });
        }

        return newArticulos;

    });

    IsBusy = false;

    MessageBox.Show("Búsqueda finalizada, pulse para ver los artículos encontrados");
    ArticulosLW.ItemsSource = Articulos;


}