Maybe you or somebody rotated rectangle?
Good thought macpawl, but hopefully the screen grab shows and makes clear that I'm using a variety of rectangles, ruling out that possibility.
For clarity: I've added flight feathers at the path starts and arrowheads at the path ends.
btw: I've just run the wonderful PathsOneDirection.js script over the paths shown in the previous grab and they now look like this:
So what is the code that makes the shape?