WPF warm AppDomain startup performance (Applicatio

I have relatively simple application, but warm (second, etc.) start-up time is awful 3-5 seconds. Profiler (VS2010, CPU Sampling) shows that more than 80% of time is spent in Application.RunInternal (~40%) and XamlRader.LoadBaml (~40%) functions.

The root of the problem is that Window is created in non-default AppDomain. If I move Window creation to default AppDomain or give AppDomain unrestricted permission set everything is as fast as expected.

I'm testing on:

Windows Seven x64
.Net 4.0
4Gb RAM
GeForce 9800GT 1Gb.

I'm creating AppDomain this way

var permissionSet = new PermissionSet(null);

permissionSet.AddPermission(new SecurityPermission(SecurityPermissionFlag.Execution | SecurityPermissionFlag.SerializationFormatter | SecurityPermissionFlag.UnmanagedCode));
permissionSet.AddPermission(new ReflectionPermission(PermissionState.Unrestricted));
permissionSet.AddPermission(new UIPermission(PermissionState.Unrestricted));
permissionSet.AddPermission(new MediaPermission(PermissionState.Unrestricted));
permissionSet.AddPermission(new FileDialogPermission(PermissionState.Unrestricted));

var appDomainSetup =
    new AppDomainSetup
    {
        ApplicationBase = AppDomain.CurrentDomain.SetupInformation.ApplicationBase,
        ApplicationName = AppDomain.CurrentDomain.SetupInformation.ApplicationName,
        DisallowApplicationBaseProbing = false,
        DisallowBindingRedirects = true,
        DisallowCodeDownload = true,
        DisallowPublisherPolicy = true,
        LoaderOptimization = LoaderOptimization.MultiDomainHost
    };

_appDomain =
    AppDomain.CreateDomain(
        name,
        null,
        appDomainSetup,
        permissionSet,
        new[]
    {
        // a few types I need
        typeof(...).Assembly.Evidence.GetHostEvidence<StrongName>(),
    });

The behavior remains the same even if I strip down XAML to empty window

<Window
    x:Class="Rosmurta.Extensibility.WpfUI.RosmurtaWindow"
    x:ClassModifier="internal"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Test"
    Height="480"
    Width="640"
    WindowStyle="SingleBorderWindow">
    <Grid>
    </Grid>
</Window>

Not too much to parse by XamlRader.LoadBaml, but it spends more than 30% of startup time event for empty window.

I've tried (and it did not help)

Adding <generatePublisherEvidence enabled="false"/> to App.config.
Adding [LoaderOptimization(LoaderOptimization.MultiDomainHost)] atribute to Main method.
Adding signatures to all assemblies.

What else can be done?