If you are able to describe the effect in the way you did, it is not *just* the second harmonic! The 2nd harmonic adds a false richness, but is also easily canceled by push-pull circuitry, which is what a Jadis is.
So the source of the artifact can be caused by studio effect, cartridge issues, amplifier overload- a variety of things really. I would try the recording on other systems and see if that recording behaves the same way at lower volumes, stuff like that. I would expect that you will find out what is doing it quite quickly.