mailman-web.wsgi: 500 Internal Server Error since rebase to Django-1.8.11

Hi,

I can't run mailman-web.wsgi since it was rebased to Django-1.8.11. All i get is a 500 Internal Server Error:

[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234] mod_wsgi (pid=17980): Exception occurred processing WSGI script '/opt/mailman/mailman-bundler/bin/mailman-web.wsgi'.
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234] Traceback (most recent call last):
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234]   File "/opt/mailman/mailman-bundler/eggs/Django-1.8.11-py2.7.egg/django/core/handlers/wsgi.py", line 170, in __call__
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234]     self.load_middleware()
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234]   File "/opt/mailman/mailman-bundler/eggs/Django-1.8.11-py2.7.egg/django/core/handlers/base.py", line 50, in load_middleware
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234]     mw_class = import_string(middleware_path)
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234]   File "/opt/mailman/mailman-bundler/eggs/Django-1.8.11-py2.7.egg/django/utils/module_loading.py", line 26, in import_string
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234]     module = import_module(module_path)
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234]   File "/usr/lib64/python2.7/importlib/__init__.py", line 37, in import_module
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234]     __import__(name)
[Mon Mar 07 2016] [:error] [pid 17980] [remote x.y.z.a:1234] ImportError: No module named middleware

Any ideas what is going wrong there?

Environment: RHEL 7.2 httpd 2.4 Installed with mailman-bundler

Regards Timm