Here's one thread:
https://www.project1999.com/forums/s...ed+mobs+moving
It's super easy to replicate. Get something to run at you, and root it. Often it will appear to continue running at you (and through you and off into the distance) but the mob is actually still where you saw root land on it. Casting on it will show your spells land on the running mob, and it can even run out of range (despite still being where you rooted it) unless you do something like move within agro range of where you know it to be, or apparently strafing like BlackBellamy said.
I'll see if I can't grab a video of it happening.
-Mcoy