NPC in caves disappear

[Alaric]

NPC in caves in Eastern Kingdoms when attacked have tendency to go up into air and  disappear when they try to follow player in combat.

To date I seen this behaviour in Loch Modan and Redridge.

 

How to recreate

Attack NPC then walk few steps away.

Included is Screenshot in Stonesplinter Valley (Loch Modan) when trying to do quest "In Defense of the King's Lands" with one of targets of kill quest targeted (further than 40yd away by game reckoning from my position) but not present at it's spawn point.

Edited May 11 by Alaric