This thread happened to catch me while I was re-exploring the Sith Warrior class so I figured I'd stick with Vette. I have experimented, when finding a dialogue trigger, with switching companions out and running back over the same point to see what happens but so far have had no joy with it. Perhaps the triggers have a cooldown. Has anyone found differently?
Without testing, I would say that my anecdotal evidence supports your theory. Maybe try logging out and back in? I will do this later on my Agent and report back.