Both oils come from the same kind of tree, but different parts of the palm's fruit

(The PKO comes from the seed, the PO from the pulp.) From what I gather, PKO has a lot of the same qualities as coconut oil in soap, so while it's not a "soft" oil by any means, it doesn't give the exact same sort of hardening effect that palm oil does.
As for whether it will harden up -- did you straight up replace the PO in your recipe with PKO, or did you re-run it through a lye calc? I'm wondering if it might need more or less lye or something.... If you did recalculate, I imagine it will harden up eventually (maybe others can speak more to that), PKO should still make a hard soap

d'oh, ninja'd!
