Whilst I agree that it might not be a major security bug, I'm somewhat surprised that you've marked this as a "won't fix". MySQL is probably the database that is most likely to be deployed (does it also affect MariaDB?) Although unlikely, having new users potentially granted the rights of older users is one of those edge cases that might cause a lot of pain if triggered :(
Whilst I agree that it might not be a major security bug, I'm somewhat surprised that you've marked this as a "won't fix". MySQL is probably the database that is most likely to be deployed (does it also affect MariaDB?) Although unlikely, having new users potentially granted the rights of older users is one of those edge cases that might cause a lot of pain if triggered :(