oxyplot plotview not working

HI all, I have the following code.

        var model = new PlotModel { Title = "World population by continent" };

        var ps = new PieSeries
        {
            StrokeThickness = 2.0,
            InsideLabelPosition = 0.8,
            AngleSpan = 360,
            StartAngle = 0
        };

        // http://www.nationsonline.org/oneworld/world_population.htm
        // http://en.wikipedia.org/wiki/Continent
        ps.Slices.Add(new PieSlice("Africa", 1030) { IsExploded = true });
        ps.Slices.Add(new PieSlice("Americas", 929) { IsExploded = true });
        ps.Slices.Add(new PieSlice("Asia", 4157));
        ps.Slices.Add(new PieSlice("Europe", 739) { IsExploded = true });
        ps.Slices.Add(new PieSlice("Oceania", 35) { IsExploded = true });

        model.Series.Add(ps);

        Content = new PlotView { 
            Model = model,
            BackgroundColor = Color.Blue,
            HorizontalOptions = LayoutOptions.Fill,
            VerticalOptions = LayoutOptions.Fill
        };

it is supposed to draw a chart on my screen, however all i can see on both android and IOS is just the background color. Does anyone know why ?? Is this a known issue ??

oxyplot.xamarinforms version is 2015.1.899 -alpha

any ideas?? I'd greatly appreciate any.

thanks!