Spells: Damage over Time - DOT BUG

[Saylord]

What is up with DOT's, If the mob is in its spawn location and I root/dot it full damage takes place. However if it moves and I root it again, the game thinks the mob is still moving and only does 66% damage. I have to go into melee range and get hit then back off, the DOT resumes doing full damage. Is this a known bug, or a feature of the game now? I do not remember this being a thing.