Hi Shadowcaster, thanks I'm glad that you are liking MoI!

What you are showing there is a bug in the display engine - your actual curve is fine it's just not being displayed properly when it goes straight like that.

It's unfortunately a somewhat difficult bug to fix without causing some general performance degradation to all curve drawing if not done very carefully - that's why I have not attempted to fix it so far and actually may not attempt to fix it since it only happens in very particular circumstances (curve with minimal points and a particular "S" shape with same direction end tangents and curve midpoint right at midpoint between the line through the end points).

See here for some more description:

http://moi3d.com/forum/index.php?webtag=MOI&msg=4101.2

http://moi3d.com/forum/index.php?webtag=MOI&msg=7405.12

If it's getting in your way a lot you should be able to avoid it by using Edit > Add pt to insert a new point into the curve, you can do it with control points turned off to keep the same curve shape.

- Michael