I suspect this happens most with people using a full size keyboard and the numeric keypad - when numlock is off, they miss that the numbers didn't get entered a

I suspect this happens most with people using a full size keyboard and the numeric keypad - when numlock is off, they miss that the numbers didn't get entered and boom, there's your address instead. I suspect you never see this with people whose number-after-name was 4 or 7, because they won't be entering a valid email address.