When Paperclip initializes Paperclip::Style objects, the Style initializer removes the :format, :geometry and :processors options from the options hash and stores them as an instance variable. The args hash that is passed in to the Style initializer is a reference to the class inheritable attribute "attachment_definitions", and these three options are removed from that hash.

When Rails class caching is on, every Style initialized after the first one will not have the :format, :geometry and :processors options passed in, because they were deleted from the class. This breaks a lot of things, particularly in our case path and url interpolations for styles with different file extensions.

We've written some Rails controller tests that demonstrate this. Unfortunately I couldn't write a test in Paperclip itself to show this problem, because there is no Rails environment in the Paperclip test suite:

class Material::Video < Material
  has_attached_file :resource, {
                      :styles => {
                        :Ogg_preview  => {:format => :ogg, :codec => "theora"},
                        :H264_preview => {:format => :mp4, :codec => "h264"}
                      },
                      :processors => [:video]
                    }

end

describe Material::Video do
  describe "attached file" do
    before do
      file = fixture_file_upload("files/test.mov", 'video/quicktime')
      @video = MaterialFactory.create_material({:resource => file}, creative_works(:film1).id)
      @video_stem = "/system/resources/#{@video.id}"
    end

    it "should have an original version" do
      @video.resource.url.should match "#{@video_stem}/original/test.mov?"
    end

    it "should create H264 preview (for Safari Users)" do
      @video.resource.url(:H264_preview).should match "#{@video_stem}/H264_preview/test.mp4"
    end

    it "should create Ogg preview (for Firefox Users)" do
      @video.resource.url(:Ogg_preview).should match "#{@video_stem}/Ogg_preview/test.ogg"
    end
  end
end

The fix is quite simple, just dup the style args when initializing a new Style object (in attachment.rb line 58) so that the options are not deleted from the cached class variable.

We've forked the repository and made the fix here:
git://github.com/pivotal-creationmix/paperclip.git