Spline turns into flat segmented line

[treddie]

Howdie.
I have a datum curve I imported from an IGES file and it imported correctly as a smooth spline. But if I right-click it in the tree and select "Edit Definition", and bring up the editable .ibl file it got translated into, even if I don't edit anything and just resave it, it turns into a flat segmented curve. How can I prevent this from happening, as I need to edit the points data without destroying the smooth curve?

I am using W4

Thanks for any replies!

 

[treddie]

I noticed that when I open the text file in ProE to edit it, it breaks the spline up into individual segments. If I edit the file so that it is just a continuous sequence of points, removing each of the extra "Begin curve ! <x>" lines, all the indexes and any duplicated points, I can get my smooth spline back, but even though the coords are exactly the same, it does not match the original curve when regenerated (the nodes don't even line up). You don't notice it unless you zoom in, but you don't have to zoom in that far to notice the difference. That kind of inaccuracy is going to kill an awful lot of regens.