duplicated log lines in console

[Erwin]

my app seems to be running fine in dev mode ( Rails4, Devise, OAuth2 , Doorkeeper ) but looking at the console , I can see all log lines duplicated ....
where should I look for any tricky bug or missing param ?anyway to get more info on what's happening ?  thanks a lot for feedback

 (ruby-2.0.0@rails40)$ rails server -p 4000
=> Booting WEBrick
=> Rails 4.0.0 application starting in development on http://0.0.0.0:4000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
[2013-08-22 12:42:08] INFO  WEBrick 1.3.1
[2013-08-22 12:42:08] INFO  ruby 2.0.0 (2013-06-27) [x86_64-darwin12.3.0]
[2013-08-22 12:42:08] INFO  WEBrick::HTTPServer#start: pid=13913 port=4000

Started GET "/oauth/authorized_applications" for 127.0.0.1 at 2013-08-22 12:42:12 +0200
Started GET "/oauth/authorized_applications" for 127.0.0.1 at 2013-08-22 12:42:12 +0200
Started GET "/users/sign_in" for 127.0.0.1 at 2013-08-22 12:42:13 +0200
Started GET "/users/sign_in" for 127.0.0.1 at 2013-08-22 12:42:13 +0200
Started POST "/users/sign_in" for 127.0.0.1 at 2013-08-22 12:46:39 +0200
Started POST "/users/sign_in" for 127.0.0.1 at 2013-08-22 12:46:39 +0200

***
Successful login with email_id : {"login"=>"yves", "password"=>"[FILTERED]", "remember_me"=>"0"}
***

***
Successful login with email_id : {"login"=>"yves", "password"=>"[FILTERED]", "remember_me"=>"0"}
***

Started GET "/oauth/authorized_applications" for 127.0.0.1 at 2013-08-22 12:46:40 +0200
Started GET "/oauth/authorized_applications" for 127.0.0.1 at 2013-08-22 12:46:40 +0200

[Erwin]

[SOLVED]  issue coming from rails_12factor gem ( to be used when deployed on Heroku in production)

I modified my gem file...

# heroku recommended gem

gem 'rails_12factor' , group: :production