Because the Actor.AddSpell function does not apparently trigger the ActiveMagicEffect.OnEffectStart event I went with casting it on the target actor. This does trigger the events correctly but, unfortunately, the spell/effect does not stay on the actor. It immediately finishes and is removed, even though it's set as a constant effect.

Is there something I missed in the CK to make it actually be constant? Both the spell and related effect are set to casting type constant effect, self targeting.