Now the question becomes, "So if the thrust isn't acting on the nozzle, what is it acting on"?
It's a long time ago but if my memory hasn't faded too much are we thinking about a choked nozzle and an increase of pressure behind the nozzle and therefore the "thrust" acting on the surface area of the nozzle itself?
It's past midnight here so I'll sleep on it and get back to this in the morning.