Game Mechanics: monk fd wiping aggro in middle of mob casting on you

[falendar]

Is this classic? mob aggro you and begins to cast a spell, you fd stand run away a few feet and spell lands, weather it resists or not the aggro is wiped. I know if i stay fd while he's casting i am going to keep aggro, happens everytime, but if i stand most of the time the aggro wipes spell lands and i go on my merry way.