As you know the Twitter use the older OAUTH 1.0 protocol for the social login, instead of the others (facebook, google) what use the OAUTH 2.0. The older protocol not allowed to provide the user email address, what is neccessary to register a Joomla user. So when you click on the twitter button for the first time you need to extend the form with your email and additional datas. So this is the proper working method for the twitter social login.