There was a related issue, which was closed https://bugs.python.org/issue26715.

If virtual environment was activated using Powershell script - Activate.ps1, the Deactivate.ps1 was not created, while the documentation says that it should.

"You can deactivate a virtual environment by typing “deactivate” in your shell. The exact mechanism is platform-specific: for example, the Bash activation script defines a “deactivate” function, whereas on Windows there are separate scripts called deactivate.bat and Deactivate.ps1 which are installed when the virtual environment is created."

Way to reproduce under Windows 10, Python 3.6.4

1. Open elevated Powershell (Administrator access).
2. Activate virtual environment using Activate.ps1.
3. There is no Deactivate.ps1

Also, when the environment was activated with Activate.ps1, `deactivate` will not work. On the other hand, if the environment was activated simply with `activate` (it works) in Powershell, `deactivate` will also work.