Did the class teach you scenarios that could cause a flood?
What happens if seals don't seal or parts are installed backwards? Seems easy to mess up a reg and get it to freeflow. What would it take to get it to flood?
I am a complete neophyte to reg designs and servicing. Someone else here is surely more knowledgeable. It is not at all apparent to me how a first stage could fail in a way that admits water into the IP chamber, but I suppose anything is possible. As for the second stage, the exhaust valve seems like the most likely culprit, as I believe was mentioned upthread.