I am playing a game as America with Hot Relations set to max (the constant war helps to reduce the enevitable slowdown). Well long story short, S. Korea is at war with China and N. Korea no longer exists. I had a great defensive line set up to keep China out of Korea while I dealt with Soviet aggression in Europe. Then, without any reason, S. Korea surrendered to China. China didn't capture their capital, nor was China able to capture any territory. There shouldn't have been any fathomable reasons for S. Korea to just give up. My lines were holding. It just irritates me to no end that S. Korea would surrender like that stranding 180+ units unless I revert back to a previous save and pull out of Korea (not a bad idea if they're just going to give up anyway).
The stranding of units brings up a valid point on another subject, after an allied nation surrenders there should be a period of time (1-2 months) where units should be able to move inside that country and draw from their supplies so that a retreat is possible and those units aren't sacrificed.