Hi Niko, can you post the 3DM model file with the curves in it so I can take a look?

It's possibly just a display bug though, in some circumstances the display mesher can not quite refine things enough and with a small number of triangles things look like that. That can happen with longer but only shallowly curved pieces like you've got there.

If you go to export to a mesh format and the export looks fine, it's likely to be a display mesh related problem, not a problem in the actual surfaces themselves.

- Michael

Ok, good to know. Sadly I deleted the object or to be more specific I have deleted the problematic part, redraw it, tried again and it worked. I have attached the working file but I guess that won't be of much help.
And sorry about the very amateurish model. I am just starting with MoI.