Duplicate Email is not getting validated after couple of times

[Chandra736]

When same email id is given for registration, in the beginning it worked fine saying "email has already taken" but after couple of times the same is not working. I looked in to the code in RegistrationController.rb , this condition would fail (resource.active_for_authentication?) and else part is executed (expire_session_data_after_sign_in!
(render(:partial => 'thankyou', :layout => false) && return) if request.xhr?) this is trying to delete the user, which is wrong...!