Rooting mobs
 

Players are able to root mobs that are coming toward them step back slightly and still be in range to hits mob but not take hits for the duration of the root.

Just for clarification. The coming toward the player part is not a necessary prerequisite. It was just an example to recreate that bug easily: Simply step back until the MOB has to follow you. He is now at his maximum thread range. Root him and slightly move back. Now you can whack him and he can't strike back. Maybe my example I was a bit misunderstanding.
I tried that with different MOBs in Sebilis and it worked on all.
I can't say if this is a common problem or dependent on the race, class and/or weapon. It happens for my Dwarven Paladin with an Spear of Cauldron Souls.

Rygorr

Update: I cant reproduce that with Drolvargs in Karnor

Update: It works against coterie legos and cents in Maidens Eye

But not against goranga gatherers.

Aditionally I found another thing. If I stand above or below (eg. a staircase or something) the MOB I am fighting and move back until the MOB has to follow me I get the "Your target is to far away, get closer" despite the fact that I am still able to hit him. This will vanish when I move to even ground.