User blog comment:MDGeistMD02/Which Witch is Which?/@comment-6301921-20131123142036/@comment-3242762-20131123221343

Yeah, I covered everything, the two saves were from the same run, I basically created two different routes through the mission from about half way through, same run, same save, etc.

The only conclusion I can come to is that engaging the other witches in battle provoked the Delilah witch to join in.

She will talk to Delilah's statue, comment on the gangs, Daud, etc., then vanish like the scout.

If you ignore the room, the attack will still happen. But yeah, 99.9% certain that that witch is the trigger.

EDIT:

The one thing I didn't check was missing the first 4/6 witches completely, going straight through to the Pump. I would imagine the attack would still take place, though.