Nearly 10 years later, I find this issue still exists! What happened with the enhancement request? I suppose a workaround could be, once you've got Z, is there a way to take the original line-with-M and interpolate the M onto the line-with-Z?
> Would you want M's interpolated for [new vertices] based on existing M's or not?
I have just discovered this bug myself! How strange it still hasn't been fixed.... Can you introduce the option to interpolate M for new vertices based on existing M's? It's critical for creating graph profiles.