Well, this is an old post, so Gregg might already have the answer to this question. But, I would like the message to reply, because it could help others who stumbled upon this problem.
The reason for extending the expander in the advanced design of VS 10 is because it has a user-defined style:
<Expander Header="Layout"
IsExpanded="True"
Style="{StaticResource ExpanderStyle_Normal}">
</Expander>
, :
/
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