It appears that a some snared mobs don't flee as intended. I think this has to do with SoW possibly, though snares should overwrite the SoW. In my experience this only happened on mobs that were sowed before I started killing them.
http://www.youtube.com/watch?v=ku00ZctMc04
Once he hits low health he starts to teleport around. It's like he's still running at SoW speeds but the animation shows a fleeing and snared (stationary) mob. Sometimes the mobs teleport to such a serious degree that I lose them and can't even find them until they regenerate enough to come back for me.