Mecanim ik + musles

Hello, I’m using Mecanim in Unity 4.3.0f4. I have humanoid rig with adjusted musle settings (for example, no more than 40 degrees left-right spine twist). Also I am using Mecanim IK (Animator.SetLookAtWeight + Animator.SetLookAtPosition). IK function doesn’t respect muscle settings: it easily rotates charachter up to 360 degrees. Is it normal scenario or a bug?

Update. I wrote to support and their answer was that it’s a normal behaviour.