Game Mechanics: Caster mobs not regaining mana?

[quenyar]

I seem to be experiencing this: When a caster mob has been up for at good amount of time, it "runs out" of mana and will not be able to cast on you. If you aggro a caster mob right after it spawns, it will have mana enough to cast on you. I think that caster mob mana regen might be off.

I've experienced this in many places, most notably in Droga where almost every mob is supposed to be a caster. Camping the Warder by clearing the dining room, and not once did any of the casters cast on me on the first round of ph clearing.