Flash of Light causes fleeing mobs to warp uncontrolably.
 

Use flash of light on a mob. If the mob flees, it proceeds to warp over and over again. Completely duplicatable.

It has an effect like fear on NPCs. It was changed in the past to act this way.

Yes, but warping - I mean pathing the same path over and over. Walk take 5 steps, WARP back to start - repeat.

The warping part intentional? Just makes it very hard to finish off - as you chase and it warps..

Since the last patch (or maybe two patches back) something similar occurs occasionally with non-blinded mobs. The client shows the mob fleeing in a particular direction, after a few steps the mob will warp to a position the fits with it fleeing in a direction 90-180 degrees different from the mob's facing. This will repeat until you root the mob or kill it with ranged attack (very difficult to get melee damage, basicly you have to be waiting at the warp-to loc and swing when the client & server sync the mob location.)

Seems likely to me that this is the same thing the OP is seeing with Flash of Light (I quit using Flash of Light some time ago because of bizarre pathing/aggro shit creating trains when engaged mobs would take off running because somebody not at the top of the aggro list happened to move to a location with bugged pathing.)

Sounds the same to me.

Depends where you flash of light the mob.

It can be dangerous spell to use if someone isn't right up against it always.

This warping its also happening with undead mobs being fear kited. Everything goes smoothly until the mob hits flee health (even though they're undead and don't flee). They will warp forward in their current direction, turn and warp again. This will continue as long as it's still feared until it dies.

Try reading my post again. It can be dangerous to use even if the char on top of the hate list is on top of the mob along with a couple other melees high up the hate list. Weird shit happens with blinded mobs when anybody on the hate list moves to a position that mob can't path directly to, apparently due to screwiness in the pathing behavior that usually (but not always) involves sloped terrain.

I noticed this behavior with the same patch that made NPCs slooowly turn to flee. If I fear the mob as it is turning, but not yet fully turned, I get this warping. Probably the same thing.

Its as if the client sees it going in one direction, but the server thinks the turn was completed. So when the client gets updated, it warps to that spot, but then continues in the direction the client thinks it is pointed in.

I can confirm that this is still a problem. If a mob gets to the point of fleeing and flash of light has not yet worn off, it will start teleporting all over the place (not like fear at all). Starting to become a serious hassle for my paladin and his groups.