- last post: 01.01.0001 12:00 AM PDT
Heh. I found one on Normal like this, and like you just explained, it disappeared at some checkpoint.
Later, on another Campaign run on Legendary, I found a Brute in a Ghost once, between Uplift Reserve and the next beacon, sniped him, stole the Ghost, and I kept it all the way through the Campaign up to the entrance of Data Hive. It wasn't disappearing between saves.
I wonder if something, some achievement, performance or action triggers this, or if it's completely random.