It has a certain amount to do with when you apply the extra -n. As I said, you supplied the reason, I explained the convention. And so between the two of us, we licked the platter clean.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'