Failes to enable plugin with trac 0.11.3

[superna@…]

Traceback (most recent call last):
  File "/local/engine/trac/trac/web/api.py", line 367, in send_error
    'text/html')
  File "/local/engine/trac/trac/web/chrome.py", line 688, in render_template
    data = self.populate_data(req, data)
  File "/local/engine/trac/trac/web/chrome.py", line 596, in populate_data
    d['chrome'].update(req.chrome)
  File "/local/engine/trac/trac/web/api.py", line 194, in __getattr__
    value = self.callbacks[name](self)
  File "/local/engine/trac/trac/web/chrome.py", line 464, in prepare_request
    for category, name, text in contributor.get_navigation_items(req):
  File "build/bdist.linux-i686/egg/TracBuildbot/web_ui.py", line 33, in get_navigation_items
    yield 'mainnav', 'buildbot', Markup('$$REMOVED$$Buildbot$$', self.env.href.buildbot())
LookupError: unknown encoding: /trac/linux/buildbot

[superna@…]

Note, the $$REMOVED$$ part is because the ticket system detected the a href link as spam...