This bug is still present in version 6 once a mob spots you thats it there is no getting away because they viewing radius increase like 10X so they will always follow you now matter how far way you get from them

UPDATED 11 October 2012: Ive taking some screen shots of a zombie that I got Aggro on me, as you can see it gets closer and closer, on some of the images where it gets really close, you'll see some zombies off to the right quite close to me all they do is ignore me because they arnt aggro!