I watched this tutorial and I wasnt able to reproduce the effect until I mirrored the half-circle. Why is that? It doesnt make sense for me.
Paths, have a direction! One of the points is first and one of the points is last. When you rotate you end up with a different shape than by mirroring by point order. If you now blend midpoint to midpoint it assumes default direction and thus you get a different blend. The other you expect the other loops in on itself.