@Maylander: Oh, Scarpetta is the trigger. That's valuable information, thanks! Maybe I'll try reloading and trying the "have Scarpetta fight Garcia and then lure more people in to fight Scarpetta" method, although won't the natives become hostile to me after they kill Scarpetta? (Scarpetta turns hostile to me once he kills Garcia.)

That really was a game-breaking bug for me.