Standard issue - it's to do with Rails not picking up icons.png when you're deploying to the production server. We got the icons working using the preceding tutorial:
#/lib/tasks/ckeditor.rake
require 'fileutils'
desc "Create nondigest versions of all ckeditor digest assets"
task "assets:precompile" do
fingerprint = /\-[0-9a-f]{32}\./
for file in Dir["public/assets/ckeditor/**/*"]
next unless file =~ fingerprint
nondigest = file.sub fingerprint, '.'
FileUtils.cp file, nondigest, verbose: true
end
end
#config/environments/production.rb
config.autoload_paths += %W(#{config.root}/app/models/ckeditor)
config.assets.precompile += Ckeditor.assets
config.assets.precompile += %w(ckeditor/*)