Hi Morten,

> Why is this?

The technical reason is that a helix or spiral is not able to be represented with a 100% exact NURBS curve unlike a circle or an ellipse for example.

So because of that the helix is created through a kind of approximation and fitting process.

It looks like there may be a bug in that special helix fitting process that gets magnified when you have only 1 turn, I'll take a look at that.

- Michael