Two bugs in regards to World's End.
Neither killing Vetrar, nor clearing all of the zone causes the border to drop. You can never setting the area.
The second one is weirder. In the image below I've circled a square in the center of World's End, right next to where I killed Vetrar. I've lost three pioneers as they walked through this square. There are no monsters or enemies. I've walked my sovereign through the square and nothing. Every monster in World's End is dead. But three pioneers have fallen over dead, in their post-battle defeat animation. No idea what's going on.
Edit: The first pioneer was solo. The other two were in a group together.
Edit2: Just tried it a fourth time. Same result, probably 50 or 75 turns later. Save game here.