Take a normal follow button with a username from https://about.twitter.com/resources/buttons#follow
Put it inside normal bootstrap dropdown like this http://jsfiddle.net/dJDHd/417/ and it will render without the username.
Please note there is another instance of the follow button below the dropdown that renders correctly although they use the same source code.
EDIT I am using latest Chrome (38.0) on OSX. The issue does not manifest on latest Firefox.