Strange NPC behaviour: Spiders and goblins fight each other (very slowly) in turns while I am not in combat.

I wanted to free the spiders from the pit in the goblin temple. But the spiders were looking to the goblins so I could not sneak and unlock the door without alarming the goblins. I went to the room above the pit and shot at the closed door between spiders and goblins. The door was gone, nothing else happened.
Then I played around to see what is possible. Wyll sommoned a cat familiar and I used it to pull one goblin after the other into another romm in order to kill them without starting a big fight. It worked. One time my cat used her ability in a position were she attracted the spiders and the goblins in front of the spiders. All of them went to the cats position, then they walked back. When they reached their original position the spiders and the goblins started to fight each other while my party was not in combat. I could see the initiative rolls and then they attacked each other one after the other. The spiders also attacked the zhent merchants.

If the spiders hate the goblins, why don´t they attack once the door is open.
I see no reason why they would only attack another when both leave their position and then return.

note: Could somebody test if the fight also starts when you only pull out the spiders with the cat, without influencing the goblins.
I am already past this point and have no old save.

groovy Prof. Dr. Dr. Mad S. Tist groovy

World leading expert of artificial stupidity.
Because there are too many people who work on artificial intelligence already :hihi: