Thumbnails are not shown and not uploaded in S3

I just setup this module in a brand new EC2 instance on AWS on a new installed Drupal 7.
I installed this module and the related modules.

First test:
I update a user profile picture, the image is well uploaded in my S3 bucket.

But on the front side, the image returns a 404 because the URL is not rewritten to my S3 bucket.
The profile URL in the website is like:
http://MY-EC2-BUCKET.compute.amazonaws.com/system/files/styles/thumbnail...

But I guess it should be:
MY-S3-BUCKET.s3.amazonaws.com/pictures/picture-1-1397551137.png

If I create a content type and upload an image, it is working. But not the thumbnail as well.

I guess it is not related, but I use nginx with this configuration: http://wiki.nginx.org/Drupal