So it doesn't depend on which spell the monster casts? Could it be continuing on from a previous 'target self' instruction? The Targeting would need to be manually set again after a target self command. If it's not this it sounds like something is broken... But if you can isolate a case of it happening and then post the AI script that might help identify why it's happening.
We are born, live, die and then do the same thing over again.