3d Curve Intersections

Im trying to intesect 2 curves

I construct my 2 curves

Handle(Geom_Curve) curve1 = BRep_Tool::Curve(E1, first, last);
Handle(Geom_Curve) curve2 = BRep_Tool::Curve(E2, first, last);

and then I construct ExtremaCC..

GeomAPI_ExtremaCurveCurve ecc(curve1, curve2);

then I check for NbExtrema to see if I have an intersection.

The problem is that this test returns false positives, that is the curves that I am intersecting are perpedicular to each other and do not interect with each other but the NbExtrema from the GeomAPI_ExtremaCurveCurve is 1, should I be using a different object for this, or query the GeomAPI_ExtremaCurveCurve class differently.

Any help is greatly appriciated

Thanks
Matt