Cajungirl, I did understand that this was the mechanism of the near-miss. I was wondering how the air-traffic controller made such a mistake.
The same way anybody else makes a mistake. When you get a hamburger instead of the cheeseburger you ordered at McDonalds, it not as big a deal though. The person making the mistake was usually distracted. The garden variety idiots usually get sorted out pretty quickly, especially in air traffic control.