WizardPage in a separate xaml file

I am evaluating the wizard product. I want all my WizardPages to be in separate xaml files and I will add them into the main wizard window as appropriate.

So created a new user control and changed it to use WizardPage rather than user control. e.g:
<Wizard:WizardPage x:Class=

Unfortunately the ever helpful visual studio 2008 SP1 designer now refuses to display the page with the following call stack:
Object reference not set to an instance of an object.
at cz.a(ModelItem A_0)
at ActiproSoftware.Products.Wizard.Design.WizardPageTaskPane.a()
at ActiproSoftware.Products.Wizard.Design.WizardPageTaskPane..ctor(EditingContext A_0, ModelItem A_1)
at ch.b(ModelItem A_0, DependencyObject A_1)
at ActiproSoftware.Products.Windows.Design.PrimarySelectionAdornerProviderBase.Activate(ModelItem item, DependencyObject view)
at ch.a(ModelItem A_0, DependencyObject A_1)
at Microsoft.Windows.Design.Interaction.AdornerProvider.InvokeActivate(EditingContext context, ModelItem item, DependencyObject view)

Whilst I never use the designer for editing because it is so useless, I do find it useful to be able to see what pages will look like without compiling. Is there a way that I can do this using WizardPages?

...Stefan