The 4th night free benefit wasn't working for me when I tried booking it online myself (nor with the change reservation workaround described earlier in the thread). Someone had problems getting reps to book it for them, but I had a helpful rep who booked it no problem. He did say before trying that usually it won't be able to when there isn't enough points for the 4th night (which we know is false, but whatever), but he was able to book it. So hopefully this means that reps know how to book the 4th night free now.