I noticed that the thumbnail files are still retaining their pdf extension. Judging from debugging it looks like it has to do with the second to last line in the thumbnail_name method.

  # Gets the thumbnail name for a filename.  'foo.jpg' becomes 'foo_thumbnail.jpg'
  def thumbnail_name_for(thumbnail = nil)
    return filename if thumbnail.blank?
    ext = nil
    basename = filename.gsub /\.\w+$/ do |s|
      ext = s; ''
    end
    # ImageScience doesn't create gif thumbnails, only pngs
    ext.sub!(/gif$/, 'png') if attachment_options[:processor] == "ImageScience"

    # Change the output extension if PDFs are being converted
    ext = ".png" if attachment_options[:thumbnail_pdf_files] && respond_to?(:parent) && parent && parent.pdf?

    "#{basename}_#{thumbnail}#{ext}"
  end

When running through the debugger, it looks like at the time of naming, the parent is not yet available causing the extension to be left as pdf.

thx.

-karl