Is the expander messing me up here?

I have to admit I'm a wpf,c# and oxyplot newbee -

When my application Starts up I don't want a visible Chart as there's nothing that's been processed. I thought I can "hide" the Chart in an Expander - (simple minded, perhaps). The following code appears to break OxyPlot? I expect at Minimum to see the Title - but I end up not seeing anything. Without the Expander I do see the Chart with Title.

<StackPanel Grid.Row="0" Grid.Column="4" Orientation="Horizontal">
   <Expander ExpandDirection="Right">
      <oxy:Plot Grid.Row="0" Grid.Column="4" Title="Plot"
         x:Name="ChartPlot" Title="Ein Grafik" 
         Model="{Binding PlotModel}">
      </oxy:Plot>
   </Expander>
</StackPanel>

What don't I understand about either the Expander or the OxyPlot control? Or perhaps there are "better practices" to hide Content until it's ready for viewing?

Thanks.