Installing PySide with pip fails

When installing PySide using pip (Linux Mint) the installation almost finishes, but finally I get a runtime error:
RuntimeError: Can't find '/usr/bin/pyside_postinstall.py'

As a result, no Qt modules can be imported (rpath problems?).

The reason is that the installation is done into /usr/local, and not into /usr. When I run the same postinstall script from /usr/local/bin manually ("sudo python3 /usr/local/bin/pyside_postinstall.py -install"), it works, fixes the rpaths, and PySide starts functioning.

The attached files are, respectively:
pyside.log – an installation log (the bug has been reproduced on another computer running the same OS version);
failure.log – an import error that happens when running pyside-uic (or any other app that imports PySide modules) immediately after installation;
how_to_repair_installation.log – a command that repairs everything.