Interesting twist on NPCs leaving the mission area

so there I am, doing a critical and (while low on health) I happened to go stand in the corridor. usually when NPCs run off to 0,0 they do it when you're otherwise engaged like fighting or whatever - this time, the door opened while i was hanging round outside and four or five NPCs stroll out, single file, right past me and down the stairs. i followed them out, shot at them while they carried on with their march before they arrived at a building about 150m away. they went inside, opened up the lift and....completely vanished. i checked all ten floors, and they were gone.

this building wasn't at 0,0 either. just some seemingly random place.

seen that happen before?