WPF WebBrowser in DocumentWindow dissappears when rafted

I'm trying to use the WPF WebBrowser control (not the winforms version) and whenever I raft the window the browser content disappears; when re-docked it re-appears. I've seen that there is documentation on using the browser window in winforms, but not the wpf browser control; I'm pretty sure this is a bug. Anyone know a workaround?

Thanks
Marc

The code I'm using:

<Grid>
<docking:DockSite CanDocumentWindowsRaft="True" UseHostedAutoHidePopups="False" >
<docking:Workspace>
<docking:TabbedMdiHost>
<docking:TabbedMdiContainer>
<docking:DocumentWindow Title="Text">
<StackPanel ><TextBlock>Hello</TextBlock></StackPanel>
</docking:DocumentWindow>
<docking:DocumentWindow Title="Web browser">
<WebBrowser x:Name="browser" Source="http://www.google.com" />
</docking:DocumentWindow>
</docking:TabbedMdiContainer>
</docking:TabbedMdiHost>
</docking:Workspace>
</docking:DockSite>
</Grid>
</Window>