Why are the Roknari Quadrene and the Chalions Quintarian?

Question

In Lois McMaster Bujold's The Curse of Chalion, one of the primary differences between the Five Kingdoms and the Roknari is their faith. While both faiths worship the same gods, the Roknari Quadrene only worship four of them (Father, Mother, Son, and Daughter), while the Chalion Quintarians additionally also worship The Bastard. Is it known how this came about?

Answer 1

The Curse of Chalion itself doesn't talk much about Roknari theology (understandable: the only actual Roknari we meet, i.e. not just hear about from Cazaril's recollections, is a Quintarian). Paladin of Souls is where you're more likely to find an answer.

"And so was born the last god, the Bastard, love child of the goddess and the great-souled demon. Some say He was born on the eve of the last battle, fruit of a union upon Her great couch, some say the grieving Mother gathered up the great-souled demon's shattered dear remains from the stricken field and mixed them with Her blood, and so made the Bastard by Her great art. [...]

"What is certainly a lie," dy Cabon continued in a suddenly more prosaic, not to mention irate, tone of voice, "is the Quadrene heresy that the great-souled demon took the Mother by force and so engendered the Bastard upon Her against Her great will. A scurrilous and senseless and blasphemous lie..."
_{Paladin of Souls Chapter 3 (pp.43-44 of the paperback edition)}

So it looks like the root of the schism was a disagreement about the nature of the gods, i.e. whether a demon can defeat the will of a goddess.

What I haven't been able to find is any mention of the history of the schism: the furthest back Bujold goes is Fonsa's struggles with The Golden General, which is only a couple of generations ago.