Hi, I am 99% sure this is a bug. Also, spoilers.
In Arx Sewers, when I enter the room with the Children, I am stopped by big Tomorrah. I successfully pass the skill check, talk to her a bit (no option to mention the painting for some reason, but that's besides the point), and she tells me not to touch any of their stuff (Implying I am free to roam their hidout).
Now, As soon as I make another two steps, I immediately get a -5 Rep with her, and she calls in her trolls to attack...
I tried it a few times. I am sure I don't touch anything. I am sure that my weapons are sheathed. No summons or anything strange with me. Just two steps toward her AFTER passing the check and she goes hostile (or rather, the trolls do, she runs away).