Lars,
I recently tried to create a trianglulated surface using a combination of points and 3D Polylines. Everything appeared to work fine, except that I noticed it produced additional 3D Faces that connected points that where clearly not adjacent, hence these additional faces crossed over the trues TIN.
The additional faces all tend to be oriented in the same direction. All connect points on 3D polylines. I've coloured the additional faces in green on attached image.
I've never seen this before, would you know why it's happening?
Regards