It's possible to build a pex with multiple versions of the same package

[wickman]

$ git clone https://github.com/sphinx-doc/sphinx && cd sphinx
$ pex . -v
  snowballstemmer 1.2.0
  MarkupSafe 0.23
  Jinja2 2.8
  six 1.9.0
  Babel 2.0
  Sphinx 1.3.1
  pytz 2015.4
  alabaster 0.7.6
  Pygments 2.0.2
  sphinx-rtd-theme 0.1.8
  Sphinx 1.4a0.dev20150811
  docutils 0.12

Note the two copies of sphinx pulled into the environment. This messes with things like PEX_SCRIPT which expects to see just one version of an entry point.