trac-admin upgrade not working

[domma@…]

I tried to upgrade from 0.7.x to 0.8. trac-admin path_to_env upgrade tells me, that the database is already up to date. In the function do_upgrade in trac-admin.py I get 3 for the current and latest version. I checked trac.db_default in a 0.8 version and in a 0.7 version. Both contain 3 as the default_version. If I try to access the updated version, I get the following error:

Traceback (most recent call last):
  File "C:\Python23\Lib\site-packages\trac\core.py", line 525, in cgi_start
    real_cgi_start()
  File "C:\Python23\Lib\site-packages\trac\core.py", line 520, in real_cgi_start
    dispatch_request(path_info, args, req, env)
  File "C:\Python23\Lib\site-packages\trac\core.py", line 435, in dispatch_request
    module.run()
  File "C:\Python23\Lib\site-packages\trac\Module.py", line 41, in run
    self.render()
  File "C:\Python23\Lib\site-packages\trac\Wiki.py", line 290, in render
    self.add_link('alternate', '?format=txt', 'Plain Text',
AttributeError: WikiModule instance has no attribute 'add_link'

[domma@…]

After removing the old trac install completely and running a new upgrade, everything works fine now. Seems like some files don't have been replaced. Don't know why this happens on windows with admin rights!?