[BUG?] ignore (some) inheritance if __init__.py is empty

I try to use Doxygen with Python-code. But I have some problems with
the inheritance and how this is displayed in the generated docs.

I generated documentation with Doxygen (in default configuration) for
the code below. But the problem is that a.ABase in the inheritance tree
of B-docu is not linkable/clickable. Even when you look at the tree for
a.ABase the class B is not shown.

This depends on the existence of the __init__.py file. I don't know
why. When I delete the __init__.py everything is fine.

This are the files

[__init__.py]
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
[/__init__.py]


[a.py]
# -*- coding: utf-8 -*-

"""
    classes of 
"""

class ABase:
    """
    bla
    """
    pass

class A(ABase):
    """
    bla
    """
    pass
[/a.py]


[b.py]
# -*- coding: utf-8 -*-

from .a import ABase

class B(ABase):
    """
        bla
    """
    pass
[/b.py]
-- 
-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v1
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=PGP9
-----END PGP PUBLIC KEY BLOCK-----

------------------------------------------------------------------------------