Well, i somtimes get it afther buying a tarot card.
Also somtimes when my nation killled the Bifrost Molument.
Also when my party wins the ED.
I think its maybe not a bug, i think it maybe have somthing to do with that Knight Online Forever story line, that when u do somthing right ingame that u get a small reward.
I would say, evry one who is intressed in this topic, watch evry step u make before getting the hp, maybe we can find out if its a bug or somthing from what i am thinking .