The email preference that you edited is not the login information that is being used to log in, but the main contact email that Stack Exchange would use to contact you (newsletters, notification digests, etc).
If you want to modify your previous login method, you need to remove it from Profile > Edit Profile & Settings > My Logins instead of Edit Email ...
I think you're confusing two things together:
(1) Email Settings
(2) Your Logins
Email Settings lets you set the preferred contact address. If you add additional email addresses to your logins and set StackExchange login passwords you'll have to delink those logins from your account separately.
If you mean the email preference information in Email ...