When you copy a path that has corner components on “normal” nodes and on “special” nodes (the ones on path intersections), the copy has only the “normal” corner components, but not the other ones.
The lost corner components are then still sticking at the original path, but with a blue highlight as circle instead of the shape the corner should have.
It is frankly quite frustrating how buggy corner components still are. I never manage to get a project done with them without having all kinds of weird issues with them.
This could be interesting for debugging: The only way I can get these corners is by exporting as OTF. When I open that, everything is decomposed as expected.