Yeah, this is true. Hostility is something of a mixed bag, some will be hostile and others will attack. Seems random, not based on their type. And they may become hostile later -- the lag time like you say.
I've seen the same thing with goblins and bandits, actually. partially aggressive groups, might be able to talk to a leader for a little bit before his aggro minions show up to fight -- or a minion might stand idle while I fight his boss to the death.
Been having a rough time with my vault delving attempts. Recent one went like this. Promising start:
Finally generated a world with some vampires in it (somehow increasing the curse count in the advanced settings caused none to exist) but they were all roaming the wilderness after having been run out of town.
Found one hanging out near a bandit camp in a black sandy waste, and the fight was going pretty well. That is until I licked his blood off my +iron halberd+ in the middle of the fight, then it became a simple execution.
Hoofed it to the local necro tower with my crew, told them to wait outside. Zombies still managed to come out and kill them, even with what I thought was a reasonable distance. Ah well, they were getting angry at me for some reason anyway (wanted to dissuade me from some course of action, though they did not say what).
Walked in to a one level high-ceiling tower, read the tablet, raised the necromancers, went outside and rescued one that had escaped alive and recruited him. All pretty good.
Nearest vault is pretty close, so went to check it out. The mid-level weapon masters were made of ash and went down easy, the low level guys had physical bodies but my handful of zombies made quick work of them. An accidental dodge/fall really messed me up, and had to take an hour to heal. Thirst set in pretty bad, and had to back out to feed on some wildlife.
Eventually found the boss creature, and man it kicked my ass. Brutally. Smashed all my zombies to pulp, and had me on the ropes. Had to climb a wall to get away where it wouldn't follow, and recuperate.
Came back with a horde of reanimated divine servants and their animated decapitated heads, and swarmed the bastard. It eventually bled out, and I reanimated it so now I have a undead divine megabeast following me.
Unfortunately, I cant find the tablet ANYWHERE. I swear I've been through the whole place, but it is hard to tell as my hoard of minions pollutes the map with spam and I cant tell were the stairs are after I've been through. Might have to resort to paper mapping?
Any tips for exploring these things?