It's even worse! Their website is so broken you can't change your password (new password fields are disabled) and you can't set a new email address as primary (the "make primary" button only appears when the new email address field is empty). Also, if you first add a new email address, save, then set it to primary, it disappears. Wtf.
I see no recourse other than closing my account, if that's still possible.  No, not even that is possible.
After adding the email address and clicking save, logging out, and logging in, I found the email address was successfully added. At this point I could change it to the primary one, click save, paste my password, and click the button on the password prompt to successfully change my primary email address. If I tried to add the email and make it primary in one session, it would not work. If I entered my password and hit enter, it would not work.
The site is very buggy indeed. But it is possible to change the primary email adress if, when you are prompted to retype your password, you "type password and click button by mouse, not by "Enter" key" (as the post says). Maybe that would work for you...