You will find many rhino commands are more robust than gh. Most likely because Rhino has had many more years of development. Grasshopper uses rhinocommon which is not always the same level of advancement as rhino itself. Here is whats currently available for sweep in rhino common. http://developer.rhino3d.com/api/RhinoCommonWin/html/Methods_T_Rhino_Geometry_SweepOneRail.htm
My guess is rhino moves the curve seam to the first profile for the sweep behind the scenes.