logout with ref on a non public page results in a "bad gateway"

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/lib/python3/dist-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1478, in full_dispatch_request
    response = self.make_response(rv)
  File "/usr/lib/python3/dist-packages/flask/app.py", line 1577, in make_response
    rv = self.response_class.force_type(rv, request.environ)
  File "/usr/lib/python3/dist-packages/werkzeug/wrappers.py", line 827, in force_type
    response = BaseResponse(*_run_wsgi_app(response, environ))
  File "/usr/lib/python3/dist-packages/werkzeug/wrappers.py", line 57, in _run_wsgi_app
    return _run_wsgi_app(*args)
  File "/usr/lib/python3/dist-packages/werkzeug/test.py", line 855, in run_wsgi_app
    app_iter = app(environ, start_response)
TypeError: 'tuple' object is not callable