WPF: Using the expander control

I need to design a user control  that has an expander  at the top of the control that is used to reveal some details about the current page being displayed. Below the expander is a ListView control displaying the content.

This is an outline of the XAML I have right now:

<UserControl>
      <StackPanel>
            <Expander>
                   ... expander content
            </Expander>
            <ListView> .... </ListView>
      </StackPanel>
</UserControl>

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The StackPanel is set for vertical mode and the ListView is stretched to fill the space left after the Expander. The issue is that the ListView does not fill the vertical space left.

To try and figure out the problem I made a test application that has a StackPanel with only a ListView in it and the same happens, the ListView does not fill the StackPanel vertically, in spite of being set to stretch.

Is there some way to overcome this please?
Sid.