Game Mechanics: Mobs not Fleeing?

[Baler]

(I'm not talking about undead or other special mobs)

Why do mobs not always flee from combat when they get near low health.
Sometimes the mob runs to the player gets close then flees.
Sometimes the mob runs to the player, hits the player then flees.
Sometimes the mob runs to the player, the player hits the mob again and then it flees.
Sometimes the mob does not flee at all.

I believe that it was not like this until recently, probably last couple patches or so.

If anyone else has been experiencing similar issues with mobs that are supposed to flee at low life and don't please share with as much detail as possible.

Edit: I'll watch for anything that can be of use to reproduce this. I've just noticed it happening often on several occasions.
The last time that made me post this. I was fighting a mob hit it with a DD spell taking it's health down to 1% and it did not flee & was a mob that flees when low on life.