issue in "striking off the chain"
It is the same with all foes in the game. If you pull them to far from the spawning point they return and regen their health, and with a good reason. Otherwise some idiots can pull all spawns in the map to one point and ball them up together, making the map unplayable for anyone.
So your not unlucky and it’s not a nasty alien-like easter egg. Just remember when kiting any enemy to kite in circles near their spawning point instead of just away.
Arise, ye farmers of all nations
Arise, opressed of Tyria!
Arise, opressed of Tyria!
Sometimes the leach, as the community seems to call it, triggers for no good reason.
There are two conditions that can trigger it, distance from spawn and if it think you are unreachable by whatever attacks the mob has available.
The second trigger seems to be what is causing a whole lot of grief.