CurveBrepIntersect problem in GH Python

HI

SO I am trying to group a large set of polylines depending on if they intersect or not a section of a surface. I did manage to do this in rhino python succesfully but now I am trying to take the script to Grasshopper python. It seems that the command CurveBrepIntersect is insisting that ALL the polylines are always intersecting each section of the surface, which is wrong. 

From the grasshopper, one of my inputs is a list of untrimmed (or trimmed) breps (or Surfaces) and I intersect all the polylines to each surface. I expect some polylines to intersect and other to not intersect, and according to this I can then group the polylines in relation to the surfaces sections. For some reason in the GH Python, rs.CurveBrepIntersaction is ALWAYS giving an intersection value for all the polylines. I understand that if there is no intersection, rs.CurveBrepIntersection will return an empty list but it seems that in GH_python that is not the case.

Any ideas why is this?

here is a screenshot so you understand better. Any suggestions welcome!!

thank you!!

Federico