UseHostedAutoHidePopups breaks under .NET 4.0

<Window x:Class="DotNet4DockingTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:shared="http://schemas.actiprosoftware.com/winfx/xaml/shared" 
    xmlns:docking="http://schemas.actiprosoftware.com/winfx/xaml/docking" 
    xmlns:themes="http://schemas.actiprosoftware.com/winfx/xaml/themes" 
        Title="MainWindow" Height="350" Width="525"
        themes:ThemeManager.Theme="AeroNormalColor"
        >
    <!-- DockSite -->
    <docking:DockSite 
        x:Name="dockSite"
        UseHostedAutoHidePopups="False"
        >
        <docking:DockSite.AutoHideLeftContainers>
            <docking:ToolWindowContainer>
                <docking:ToolWindow Title="Tool Window 3" />
                <docking:ToolWindow Title="Tool Window 4" />
            </docking:ToolWindowContainer>
        </docking:DockSite.AutoHideLeftContainers>

        <docking:SplitContainer>

            <!-- Workspace -->
            <docking:Workspace>
                <docking:TabbedMdiHost>
                    <docking:TabbedMdiContainer>
                        <docking:DocumentWindow Title="Document1.txt">
                            <TextBox Text="Moving a toolwindow will crash in .NET 4.0 Beta 2. So will opening an autohide toolwindow." />
                        </docking:DocumentWindow>
                    </docking:TabbedMdiContainer>
                </docking:TabbedMdiHost>
            </docking:Workspace>

            <docking:ToolWindowContainer>
                <docking:ToolWindow Title="Tool Window 1" />
                <docking:ToolWindow Title="Tool Window 2" />
            </docking:ToolWindowContainer>

        </docking:SplitContainer>
    </docking:DockSite>
</Window>