Hi Pilou, yup that is normal - you get several segments in that case because your input curve (the wavy one) is made up of several segments, use Edit/Separate on it and you can see the segments.

Each of those segments becomes its own face in the Extrusion and currently the Isect command does not try to automatically join the intersection result between different faces.

I guess I could make it do that, but all you need to do is push Edit/Join to join them yourself, they are all selected and ready to go.

- Michael