Combining MahApps.Metro and Caliburn.Micro

Well im trying to use MahApps.Metro and Caliburn.Micro together but im getting some problems

Here is my bootstrapper

public sealed class TestBootstrapper : Bootstrapper<ShellViewModel> 
{
    private CompositionContainer container;

    protected override void Configure()
    {
        container = new CompositionContainer(new AggregateCatalog(AssemblySource.Instance.Select(x => new AssemblyCatalog(x)).OfType<ComposablePartCatalog>()));

        CompositionBatch batch = new CompositionBatch();

        batch.AddExportedValue<IWindowManager>(new AppWindowManager());
        batch.AddExportedValue<IEventAggregator>(new EventAggregator());
        batch.AddExportedValue(container);

        container.Compose(batch);
    }

    protected override object GetInstance(Type serviceType, string key)
    {
        string contract = string.IsNullOrEmpty(key) ? AttributedModelServices.GetContractName(serviceType) : key;
        var exports = container.GetExportedValues<object>(contract);

        if (exports.Count() > 0)
        {
            return exports.First();
        }

        return base.GetInstance(serviceType, key);
    }
}

And here is my AppWindowManager

public sealed class AppWindowManager : WindowManager
{
    static readonly ResourceDictionary[] resources;
    static AppWindowManager()
    {
        resources = new ResourceDictionary[] 
        {
            new ResourceDictionary
            { Source = new Uri("pack://application:,,,/MahApps.Metro;component/Styles/Colours.xaml", UriKind.RelativeOrAbsolute) },
            new ResourceDictionary
            { Source = new Uri("pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml", UriKind.RelativeOrAbsolute) },
            new ResourceDictionary
            { Source = new Uri("pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml", UriKind.RelativeOrAbsolute) },
            new ResourceDictionary
            { Source = new Uri("pack://application:,,,/MahApps.Metro;component/Styles/Accents/Blue.xaml", UriKind.RelativeOrAbsolute) },
            new ResourceDictionary
            { Source = new Uri("pack://application:,,,/MahApps.Metro;component/Styles/Accents/BaseLight.xaml", UriKind.RelativeOrAbsolute) },
            new ResourceDictionary
            { Source = new Uri("pack://application:,,,/MahApps.Metro;component/Styles/Controls.AnimatedTabControl.xaml", UriKind.RelativeOrAbsolute) }
        };
    }

    protected override Window EnsureWindow(object model, object view, bool isDialog)
    {
        MetroWindow window = view as MetroWindow;
        if (window == null)
        {
            window = new MetroWindow()
            {
                Content = view,
                SizeToContent = SizeToContent.WidthAndHeight
            };
            window.MinHeight = 150;
            window.MinWidth = 500;
            foreach (ResourceDictionary resourceDictionary in resources)
            {
                window.Resources.MergedDictionaries.Add(resourceDictionary);
            }
            window.SetValue(View.IsGeneratedProperty, true);
            Window owner = this.InferOwnerOf(window);
            if (owner != null)
            {
                window.WindowStartupLocation = WindowStartupLocation.CenterOwner;
                window.Owner = owner;
            }
            else
            {
                window.WindowStartupLocation = WindowStartupLocation.CenterScreen;
            }
        }
        else
        {
            Window owner2 = this.InferOwnerOf(window);
            if (owner2 != null && isDialog)
            {
                window.Owner = owner2;
            }
        }
        return window;
    }
}

This works somewhat but i get a black border around my window until i resize see image below

Why is there a black border and how can i get rid of it (If i manually resize the window the border goes away.)?