This is a normal workflow, you don't need any fix.
if email already exist you see a form with 2 options (see screenshot)
1) registerer
new user with another email address
2) link a
existing user by filling username and password
Is possible to add buttons to link account when user is already logged in by adding in any article or module the code described in "Link Existing Profile" section at
http://docs.easy-profile.com/index.php/article/social-connect-intro