Just tested an old save (about 30 hours of play back, before rescuing Wulbren). Tried the approach where Wulbren hammers the wall down and I blew up the wall for the tieflings so they could all escape to the underground boat (not the outside docks as they used in my first playthrough).
Got a cutscene I'd never seen before where we all take the boat together, then everyone gets checked for mindflayer parasites by the Harpers. Wulbren does speak to me after this, which is new.
The bug may be triggered by not taking the boat with them and not getting the Harper cutscene.
