Flow(along curve) flips profile based on point count?

Hello dear hivemind,

I found an interesting thing in Grasshopper (although Rhino gives the same results) and I’m curios if I miss something very easy. The basis is 1. a curve created with crv2view (116 controllpoints) and 2. a profile that should flow around it. Easy so far… I thought. So I made an extrusion and used “flow” in Grasshopper. Please explain to me why the extrusion flips in the middle of the curve. And why isn’t it doing that with the rebuild point numbers of 10,12,14,16,17,19,20,23,29,31?
I am very happy if you put me on the right track.

Thank you in advance,

FlowChangesDirection.3dm (254.0 KB)
FlowChangesDirection.gh (9.9 KB)

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