When using edge Rails, you should use edge Arel and edge Rack, also. Otherwise you’ll get weird bugs.
gem 'rails', :git => 'git://github.com/rails/rails.git'
gem 'arel', :git => 'git://github.com/rails/arel.git'
gem 'rack', :git => 'git://github.com/rack/rack.git'
gem 'arel', :git => 'git://github.com/rails/arel.git'
gem 'rack', :git => 'git://github.com/rack/rack.git'
