Rail Sweep and Symmetry

Created by: rendetto

I've been playing around with the new "(Mono?) Rail Sweep Surface" node trying to achieve mirror symmetry, and I noticed slight asymmetry of the generated surface although all four profile curves(green, yellow, blue and red) are perfectly symmetric about the global space Y axis. The first and last V rows of the new surface are indeed symmetric to XZ plane, but all interior control points aren't.

I couldn't find any parameter values that could correct the precision of the result. Is that possible with the current implementation?

Thanks