This is something that has been around for years, and never seemed to happen back in the day and I'm not sure exactly when it began.
As many of you know, mob dmg nearly always bounces back. You only take dmg at what seems like random, without any action by the mob. This also make melee mobs almost harmless, only ranged mobs seem to actually do anything unless you stand near a melee mob for a good period of time.
This makes many low level mobs no threat to a fresh runner. I remember when a small sewer rat as actually something to be wary of as a 0/2. Not you can stand next to one (or several for that matter) and swing away.
Is this something to do with the client and server not being aligned? It's as if the client does one thing, which is then rejected, and the server says another, which isn't acted on by the client except for the dmg. If the server says that a mob makes an attack, shouldn't that make the client perform the animation/effect as well as the dmg and the client not to do anything by itself?