Web-site Admin - User Password Setting
When setting temporary passwords for users Vivaldi thinks that you're resetting your own password and offers to save this for you.
To fix this, I suggest marking some Web-site - Authentication Credential combinations as an Admin. This would just be a Boolean that Vivaldi would store with no affect on the web-site in question. The user would need to actively enter the password manager for those credentials and to change them.
This could also mean that the password manager could store a second set of credentials for the same site which would be regular user credentials. Then the user could choose at the authentication stage if they need admin access or regular.