ansible/ansible — pull request #5493 by ferrants (2014-01-03 18:00:26+00:00)
Title: pip defaults use_mirrors to no because pip version 1.5 doesn't support -...

...-use-mirrors

pip version 1.5 doesn't support --use-mirrors, so the pip module won't work with default options anywhere that has the newest pip installed

http://www.pip-installer.org/en/latest/news.html