Transparency issue,

Hi all,
Have a look at these images:!312&parId=382E99B169B58267!136&o=OneUp!313&parId=382E99B169B58267!136&o=OneUp
It’s a part of a 3d-solid that has been constructed from d2 (the green image) by extruding it and building an encroaching edge off the contour-line that wraps around the d2-shape. The surface has been tessellated into drawable fans that neatly covers the surface without visible joints. The fan-boundaries has been marked out with black lines.
The two projections of the solid has two slightly different view-points. The right looks as I would expect, but the left looks as if the edge has been drawn around the fan and not along the outer contour. This error is so convincing that I’ve looked closely at the code for the mishap. The edge that wraps around the surface ARE following the outer contour - NOT the fans.

So, why does it look as if it does follow the fans?