When removing py3* packages with pkg delete the *dist-info directories in /usr/local/lib/python*/site-packages remain as leftovers. This is a problem for Pip and other modules as these *dist-info directories are used for checking if a Python module is installed.
It will not be deleted at the time of pkg-delete. However, it seems that it removed when it is empty at the time when Templates/BSD.local.dist of mtree is used.