I hadn't noticed the "subordinate" use before, but of course co-pilot is subordinate to the pilot. And in older TV shows, the credits began with a list of the stars, followed by a list of the (subordinate) co-stars.

Maybe we need to support the reëmergence of the diaeresis for clarity in pronunciation when we do not use the hyphen. We can reëducate the naïfs who have let it fall by the wayside. Too bad it only works with vowels...

@Hairy, maybe they meant "colander..."

So glad someone else noticed this. I like the "universal email" theory.