Impossible to avoid melee attacks?

I've been having trouble since beta 5 in avoiding melee mobs if they move quickly. Traditionally, the strategy is to let it run up to up and just as it begins its melee attack animation, run away and pop off some more shots. Now, however, I am getting hit by said melee attacks even though I'm 3/4 of the way across the screen before the damage occurs.

Is this a bug? Or, like WoW, is the idea that if they can start the attack then they are guaranteed a hit?

Note that I have not had even the slightest of lag issues in the beta, so that is not the cause.