I said "automatically-generated" because this is what happens during upgrade. Existing error messages were moved into the new system, with a new Custom HTML and Error Message template being generated for each existing list. Previously, error messages were stored along with the custom HTML for the subscriber error page. Now, you can apply an HTML template and/or error message template to more than one list.
Rowdy, are you sure that ALL of your error message templates have the correct response in Duplicate Email?
Trevor, no, this was not corrected in the final release. This is still an issue for anyone who downloads v1.8 now and upgrades. I plan to update the distribution ZIP today to prevent it in the future.
One thing to note is that the Default Errors will reflect the correct value for the duplicate message, but upgraded (generated) error-templates (named "List 1 Error Messages", for example) would/should not.
Regards