In the Microsoft Particles test set, 

<test group="particlesIg003" name="particlesIg003.v"/>

the instance document is described in the metadata as valid. I believe it is invalid.

The instance contains the element 

<a:e2 xsi:type="a:ext"><a:e1/></a:e2>

which is validated against the local element declaration

<xsd:element name="e2" block="restriction"/>

This is valid only if the complex type a:ext is validly derived from xs:anyType given {restriction}. Since a:ext is derived from x:base by extension, and x:base is derived from xs:anyType (implicitly) by restriction, I believe that this is not the case.