We really need to get a new thread or update the OP with new info.
But to answer the two posts above me, there are actually 2 different spreads locked in by this method. One applies to bisexual pokemon (including nidoran, probably also volbeat/illumise), and the other to monosexual pokemon (including genderless). As such, the sawk/beldum uses the monosexual spread while the magikarp test parents use the bisexual spread.
Also, in the case of genderless+ditto, ditto = female, genderless poke = male.