It has recently been discovered that there is an apparent “change” to ArchiCAD’s vector tools. Where we used to be able to inject parameters between lines, polylines, arcs and splines; in AC v18 it doesn’t seem to act the same way.
There is a solution! In the selection settings for each tool check the box that says “Uniform Settings for Line Tools“.
Quick and easy you are able to inject parameters from a polyline to a line or spline or arc. If you are not aware that this was an option, be sure this box is checked in all your vector tools selection settings and start using the inject parameters features for even more element types.