Sometimes you use a login across multiple sites. If you don't have that website stored in the login it asks if you want to save a new login. Instead, it should ask if you want to add this site to this log-in or phrase it as an update. it would then store the new site as an additional site for these credentials to be used in.

While it may not be the best practice for security, it also serves to update login sites for the same site when the address is changed.