For what it's worth, sentient aether under containment always behaves like that. There was a scene in 1.0 that showed that even if you trap a Twelveswood elemental in a jar for a few days, it's going to explode out blindly attacking anything nearby. The fact that Bahamut was summoned by a society whose state of mind was dominated by rage, vengeance, sorrow and hatred for the world of man made it that much worse.