This just happened to my game today when my party returned to the underdark exit after killing bodhi. I explored the map and there was a battle between the drows and the elves at the entrance to the cave leading to the underdark. The drow mage charmed/dominated an elf and the other elves attacked the new hostile elf. When he was dead, a very nasty elven mage teleported in. He warned me of attacking the elves and instantly killed my main character.
This is a bug because my party didnt commit a hostile action but got punished for the result. Out of frustration, I reloaded and setup some traps. It killed the spawned elven mage instantly, but another spawned on the map. It turns out that there would be infinite number spawns of elven mage.
Current Behavior: 1) Elves attack my party for the death of their brethren but the player did not commit any hostile actions. 2) Infinite Elven mage spawns
Expected Behavior: 1) Eliminate this behavior 2) Only one elven mage can spawn w/ special abilities (just like the "unkillable" thief when the player attacks the shadow thieves at their headquarter.)