There's something that should be fixed, since it lets you exploit the AI. Basically, many enemies don't care what they're targeting with their attacks and spells. For example, if you summon a fire elemental in the burning area monsters will still attack it. And heal it. It allows for sick, sick tanking and should be fixed.
I actually thought that too, at start, but then I remembered you're fighting not-so-intelligent creatures. Attacking what's in front of them is their whole point.
I believe (and hope) that when you fight intelligent enemies, like humans, they know better.