The way it is designed at the moment is that during the internal animation update, the Fire Animation Events will fire all events that occurred between the time of the last update loop, and the current update loop. There is no special case made that will stop firing events if a state machine structural change is made (for example, by calling animator.play). This means that in the user case, those two events will be called in a single update loop.
While this is not something we're going to change or fix in the current animation system, it is something that we are taking into consideration for the next one, as the use case is a valid one