AutoCAD Civil 3D :: Adding A Curve To Existing Alignment

I have an existing alignment issued to me which has been created using all straight lines even where there should be curves. I am trying to insert curves in these areas. Using free curves (2 entities and a through point) I create a curve then somethings happen I can't work out -

1. The curve is created but the original straight linework stays. I would have thought the original linework would automatically delete. See attached pdf between points 60 and 62 the curve and straights can be seen.
2. Then all stations after the curve are changed to the question mark symbol. If i click on the alignment all the grips are still there for the full length of the alignment, indicating the alignment is still in one piece.
3. If I try to create another curve further along the alignment it won't allow it. Stating on the command line "Selected entity must be part of the main entity."

I'm using C3D 2009.