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Not really, the AI is just too "smart" for its own good sometimes. It will ignore your orders if:
* There is no valid target for the spell it is trying to cast. It's not very smart about this, either. At least in dom2, it wouldn't cast for instance resist fire, if you had a 50% fire resist item, so having such an item actually made your resistance WORSE than if you didn't have it. I don't know if this aggravating problem is still around. Of course, the AI will happily try to summon soulless, even if there are no corpses...
* The AI thinks the enemy army is too weak and does not want to waste the spell.
* The AI thinks the fatigue cost would be too high for the spell (the AI will never cast a spell that puts it over 200 fatigue, and sometimes won't cast them to put it over 100 fatigue).

If you are worried about being a sitting duck, you should probably have Ritual of Returning on your pretender. This way, he won't risk getting himself killed when he is out playing mobile artillery. It's a waste of a turn if he gets stranded, but at least he won't die.