Hi Gunter, are you using an older version like version 2.52 instead of the most recent version 3 ?

There have been some fixes to flow in version 3 to prevent that type of unwanted twisting from happening.

In earlier versions you can avoid the twisting if you rotate everything by 90 degrees in the side view so that the 2 path curves are flat in the Top view rather than being arranged vertically, that should probably then flow ok for you in version 2.52 .

- Michael