I've read that their appearance can be random, but I doubt it's solely that. I've tried reentering the area maybe 10-12 times, from a point when I'm pretty sure I hadn't loaded that map cell yet (specifically, near Novac and the Toxic Waste Dump) and I always get the same result... no dying troopers, just some scattered frag mines and one solitary already-dead trooper boobytrapped with yet another a frag mine.
Seems a trivial thing to be hunting down i know... :facepalm:
