I am certainly no maths expert, but the error shows up in almost every along-path-plugin. I think where two lines intersect, there should be a stop-don't extrude any further point. After the crossing (i think even in "round corner") nothing acts like it's supposed to. Perhaps too simple where lines cross each other, where x = y then end. Depending on the function x shouldn't be allowed to be greater than y after an x = y. But I'm also not very good with code-writing... greets, kerr