When processing transactions in Online Express, constituent updates sometimes trigger if the donor enters information into the form that does not match their constituent record. Generally the dialogue box displays the entry from the form, and the Raiser's Edge value, so that the user can compare the two and decide if they want to accept or reject the changes. For some users, when the update is for emails, the Raiser's Edge field is blank, even if the constituent has an active email on their record. Additionally, even if the organization's business rule is set to warn if there is a duplicate email type, the warning may not trigger when the email update is accepted.
This has been resolved with the 9/13/16 release of Online Express.