Sorry for the mistake.

I corrected the pkgB package, but the result is the same:

    jaraco@devjaraco:~$ tree master
    master
    ├── __init__.py
    ├── __init__.pyc
    ├── pkgA
    │   ├── foo.py
    │   ├── foo.pyc
    │   ├── __init__.py
    │   └── __init__.pyc
    └── pkgB
        ├── bar.py
        └── __init__.py

    2 directories, 8 files
    jaraco@devjaraco:~$ python2.7 -c 'import master.pkgA; print("pkgA.__package__ is {}".format(master.pkgA.__package__)); import master.pkgA.foo'
    pkgA.__package__ is None
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "master/pkgA/foo.py", line 2, in <module>
        bar = __import__('pkgB', level=1).bar
    ImportError: No module named pkgB

As you can see, __package__ for pkgA is None. Same is true for master.__package__.