Usually entities are ok if they touch a world brush, but they shouldn't be inside the world brush. I guess it's a bit different for nodes, which need to be slightly above. Not noticed the problem myself before, on usually suffices.
Yeah I'm still confused how to get numerous NPCs to not go to the wrong actbusy, but I may make some of them scripted_sequence instead. But then I'll of course need to figure out how to make it so I can script walking, if possible. On a Trigger.