OnStateEnter isn't updating in the correct order with normal update?

It seems to me that OnStateEnter isnt being called in the correct order with an Update. I can prove this is happening by polling the state manually at the start of the update loop, and comparing it to a call made from a OnStateEnter state behaviour that calls back into my core script. as follows.

 void Update()
 {
     bool isLocomotion = animator.GetCurrentAnimatorStateInfo(0).IsName("Locomotion");
     if (isLocomotion != locomotionState)
         Debug.Log("UNSYNC'D");

     if (Input.GetButtonDown("Fire1"))
         animator.SetTrigger("Fire1_Pressed");
 // if I use locomotionState here, it will get out of sync and result in the release being fired incorrectly.
     if (Input.GetButtonUp("Fire1") && !isLocomotion)
         animator.SetTrigger("Fire1_Released");
 }

 // this is called by a SendMessage within the mecanim statebehaviour.
 void OnAnimationTrigger(AnimatorStateInfo stateInfo)
 {
     locomotionState = stateInfo.IsName("Locomotion");
 }

My question is, why is this happening. because in the documentation its directly claiming I don't have to poll states anymore and OnStateEnter should be accurate, it is isnt.