Quote Originally Posted by Leptomeninges View Post
I've definitely seen vassals created after RD get hit by the negative diplomatic modifier. I'm unsure if it was only after I took Kyoto. In some early games I "liberated" several vassals for trade purposes after RD and was surprised when they turned on me as I'd heard they were immune to the penalty if created after RD.
Apparently the negative diplo modifier is applied twice; once at Realm Divide and a second time when you take Kyoto. Since that penalty applies to all factions, even vassals, you can only get perfect 'loyal' vassals by creating them after both of those events have occurred.