Latent activated by Arcane Circle...this leads one to assume that the Haten Earring would be triggered by Warding Circle, and the Priest's to be triggered by Holy Circle.
I don't know what activates it and I have not done any testing nor will I, but if I were asked to make a guess at the activation, I would think it might be the same as the EXP bonus from AC + Sanction. You prob need to be in the ToAU areas with Sanction on, undecided if you would need AC or not.