Why does pip install the wrong version in my virtualenv?

Question

I created Python virtualenv with the option - system-site-packages .

But there is one package with the old version installed. The one I want to install is in a newer version with pip command .

So, I go into virtualenv and try to install a newer version. It downloads the new version, but installs the version installed on the system. What can I do?

(myvirutalenv)username@workpc ~/.virtualenvs/myvirutalenv $ pip install proteus==4.0.* --ignore-installed
Collecting proteus==4.0.*
  Using cached proteus-4.0.2-py2-none-any.whl
Collecting python-dateutil (from proteus==4.0.*)
  Using cached python_dateutil-2.5.3-py2.py3-none-any.whl
Collecting six>=1.5 (from python-dateutil->proteus==4.0.*)
  Using cached six-1.10.0-py2.py3-none-any.whl
Installing collected packages: six, python-dateutil, proteus
Successfully installed proteus-3.2.0 python-dateutil-2.5.3 six-1.10.0