StateMachineBehaviour OnStateXYZ functions

Hello,
I'm currently on 5.0.f04
I'd like to know more about OnStateXXX functions on StateMachineBehaviour class. The documentation is rather thin about it.
I use behaviour classes to place my game/animation logic into because it's neat and I don't need to have my own separate state machine running (as I did in Unity4). For this purpose, however, I need to know exactly when OnStateEnter / OnStateExit function are called.

OnStateEnter, for example, as documentation says, is "Called on the first Update frame when a statemachine evaluate this state". Other documentation page says: "OnStateEnter is called on the first frame of the state being played."

Let's have the following scenario:

State A, State B. State A plays a looping animation.. State B plays a one-shot animation. We have a transition A->B with a trigger condition. We have a transition B->A with an exit time condition.

Now, what happens if A->B transition is _longer_ then state B animation?
Exit-time condition to do B->A transition is true even before A->B transition is finished. Is it?
If yes and B->A transition begins then what happens to A state behaviour? Is OnStateEnter called when, in fact, state A is still blended (A->B transition didn't finish yet!).
Either the first nor the second documentation description doesn't provide an answer.

From my current testing, OnStateEnter and OnStateExit is called unreliably and I think it is just because the situation mention above. OnStateEnter is not called.

Do you have any experience with this?
Is there any better documentation about this topic?
Thank you.

-Martin