What the heck are lammasthas for????

[Beorne]

Ok, I've won the battle, but it has been very hard with the sacrifice of my undead and carrion cavalry countering vine ogres, and the heroic shield of my black centaurs units and my pan assassin lonely flanking itself an army of arco infantry

But the bulk of my army (a hundred of various carrions, manikins, satyrs, carrion elephants etc.) staggered back and forth all the battle. Why? Because my carrion dragon, using some of my very precious death gems, casted (as scripted) repeatedly "summon Lammasthas" that are, clearly, considereed an enemy. So I had an enemy Arco army on the front and was attecked in the rear by some winged ethereal things.
Is this a feature?
How could I successfully use that spell?