Why is attachment_fu saving everything at the same size?

Question

I have this Photo class:

class Photo < ActiveRecord::Base
  has_attachment  :storage => :s3,  
                  :content_type => :image,
                  :max_size => 500.kilobytes,
                  :resize_to => '600x600>',
                  :thumbnails => { :thumb => '100x100>', :mid => "300x300>" }
  validates_as_attachment
end

Every time I try to add a new photo 3 files get saved and 3 rows are added to the database, the problem is that each file has the same file size, and each is as big as the :thumb constraints allow.

Any ideas?