CiviCRM alters Drupal user's email address to use primary email

To reproduce:

Create a contact with primary email "primary@example.com" and secondary email "secondary@example.com"

Add a new Drupal user (via Drupal's admin interface or Drupal's registration form) with email address "secondary@example.com".

The new Drupal user will be created as expected, but the Drupal user will have the email address "primary@example.com"