Error Correction
From a registration form I'm testing

This is intended behavior?? You're supposed to put the first email in both boxes, what's wrong here?

The error message attached to the field with the bad value says to put the same (bad) value in again.

@jbhelfrich I guess it's a little obtuse, but it made sense to me anyway. It's saying both boxes should have the same value.

You understand that because of years of experience with good UI design that have taught you what an error on the password registration form means. You understand the problem despite the error message, rather than because of it. And if all users understood those things automatically, web design would be very different

Meh. Personally, I don't think the confirmation field is any use. Seems like a relic of a previous time.

Password field, maybe, with reset options. But with email fields (and I misspoke in the last comment, it's email fields at issue here) I think it's still important. Imagine a transaction that creates the user account and completed the precise at the same time, with no email confirmation. A typo in the domain of the email field becomes an instant customer support case because your customer can't login.