Hi Neo,

I have done this in T-Splines for Rhino:

>>>Unfortunately it does not look like an easy one to fix, it will probably need to wait until the authors of the geometry library that I use are able to improve it. That may take a while.

Is a pity really an old product (Solid++) to carry Bugs like that...Perhaps on of the reasons why their main client VectorWorks moved to Parasolid. I hope they sort it out soon.

Paolo all the wishes above are supported in most Nurbs software, also Rhino has most of them, so no need of T-Splines for something like That.