[vtkusers] Shadows not being created?

[David Doria]

In this wiki example:
http://www.vtk.org/Wiki/VTK/Examples/Cxx/Visualization/Shadows

it is supposed to create shadows on the plane, like this:
https://gitorious.org/vtkwikiexamples/wikiexamples/blobs/master/Testing/Baseline/Visualization/TestShadows.png

However, on my machine, it is producing:
https://gitorious.org/vtkwikiexamples/wikiexamples/blobs/master/Testing/Baseline/Visualization/TestShadows_1.png

Does anyone know what might cause the shadows not to be created?

Thanks,

David