Not to be the devil's advocate, but I seriously wonder about the authenticity behind this thread. Take no offense, Kalashnikova, but as a teacher I see a lot of kids just make something up for a hell of telling a story, and I'm wondering if this is the case here.
To back myself up I went into the Construction Set and tried to spawn in a Legionist with zero movement (like the ghosts at the Cavern of the Incarnate). I managed to do so, and upon killing him that was the end of it. Why he would respawn or "vanish", I have no idea. It may be possible (as I'm only mediocre with the manipulation of the Construction Set), but I couldn't even intentionally
code this action, so I'm wondering flat-out how.
Please don't take this as an insult to you as I may be wrong and you are right, but I just can't see why this would happen.