When pulling a mob...

[orestes]

...it starts running towards you and it ends up behind you (not really behind you but you have to take a step back in order to start attacking it). Is that a vanilla thing, a server thing, or me lagging too much?

[Armagedda]

Vanilla thing. You'd always jump back once and start killing the mob.

[Banezilla]

It's a Vanilla Mangos thing, fairly sure that wasn't the case in retail.

[fartyfart]

It is not a vanilla thing, it's an error with melee mobs that they neglected to fix.