[vtkusers] Distortions

[Jaspar,Marc,TRENTON,Engineering]

Hi List

Trying to linearly extrude a structural steel profiles.  When extruded,
extra panels are generated at both ends of the shape.  Tried counterclock &
clockwise definition but still get extra triangular panels emanating from
the origin of the definition. 
Is it due to being a concave shape or is there a work around?
Thanks in advance

Marc Jaspar