I have a series of lines and arcs that I want to join into a polyline in order to create a 3D extrude. All of the arcs and lines are co-planer and, as far as I can tell, form a closed object. When I 2D Join Polyline them, it excludes a long chain of the geometry and yields a partial open poly line. If I 3D Join Polyline them, I get the closed polyline I am looking for. Given the difference between 2D and 3D Join Polyline explained in the manual, I suspect that the excluded objects in the 2D case are somehow part of a different work plane or something that prevents them from joining, yet by every other indication, all parts are coplaner.