Sweep along 2 rails

some times the comand sweep along 2 rails create the surface in the wrong direction.
why is that … have no clue.

A few Rhino commands actually get information about your intentions depending on where you click the mouse when selecting curves for rails etc. In Grasshopper there is no user interaction.

In the image below I have created a sweep2 but there are two possible results depending on whether I select to the left of the Section Curve or to the right when selecting the first rail curve. Grasshopper must go by some preset assumption and curve direction is as good as any.