Rails: CarrierWave resize_to_ don't working in rails 3

I use CarrierWave to upload file (image)

class ImageUploader < CarrierWave::Uploader::Base
  include CarrierWave::RMagick
  version :medium do
    process :resize_to_limit => [600, 240]
  end

  version :large do
    process :resize_to_limit => [960, 360]
  end
end

In my model

class Listing < ActiveRecord::Base
  mount_uploader :banner, ImageUploader
end

When i upload a image with original size [1006, 368] after upload i have 3 version of image above (original, banner and medium), but both 3 version same size [1006, 368]. Should 3 version have 3 different size. How do i can fix this?