If I run the rs.Command("-Trim ") I get a diffrent result if I pick the curves and surface with get or just pick them on the screen.
Have tested on this file. test.3dm (290.7 KB)
import rhinoscriptsyntax as rs
if __name__ == "__main__":
inter = rs.GetCurveObject("get curve")
surface = rs.GetSurfaceObject("surface")
print rs.Command("-Trim SelID " + str(inter[0]) + " _Enter SelID " + str(surface[0]) + " _Enter")
print rs.LastCreatedObjects()
rs.Command("-Trim ")