If an email address that is already tied to an existing user is added to a Role in User Administration, a warning message will appear to the Site Administrator.
The message will indicate that an existing user was found within the system that is connected to the email address they've provided. This does not mean the account cannot be added to your system as well; it is just a confirmation.
After the warning appears, the Site Administrator can then either accept the existing User data or decline.
If the 'Cancel' button is clicked, the email input field will be blank.
If the 'Continue' button is clicked, the input fields are filled with known User data and are not editable.