logger 499 error - bug in Swift or bad code

I am not sure if it's something wrong I did or some bug. Here is the summary of what I did.

Consider the following proxy middleware - "logger-499" . This middleware does very minor things - it copy env to new variable, process the original request, than generate new request based on original env and return response back to the user.
I activate it by doing GET on some existing object . Here is the code of the middleware:
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
from swift.common.utils import get_logger, register_swift_info
from swift.common.swob import Request
from swift.common.wsgi import WSGIContext

class Logger499Context(WSGIContext):
    def __init__(self, wsgi_app):
        WSGIContext.__init__(self, wsgi_app)
        self.container_md = container_md

    def handle_original_call(self, env, start_response):
        app_resp = self._app_call(env)
        if self._response_headers is None:
            self._response_headers = []
        start_response(self._response_status,
                       self._response_headers,
                       self._response_exc_info)
        env['swift.original_status'] = self._get_status_int()
        return app_resp

class Logger499Middleware(object):
    def __init__(self, app, conf):
        self.app = app
        self.logger = get_logger(conf, log_route='logger_499')

    def __call__(self, env, start_response):
        '''
        Check the 499 error by doing GET on some existing object.
        If pipeline = ... proxy-logging logger-499... - ALL works fine. Logger prints 200 OK.
        If pipeline = ... logger-499 proxy-logger ... Then:
            Doing GET on existing object, logger will print two lines in log
            499 Error and 200 OK. Client never receive 499, only 200 OK.
        To re-solve this, I need to uncomment the # line. Have no idea why it solves it :)
        '''
        req = Request(env)
        try:
            (version, account, container, obj) = req.split_path(3, 4, True)
        except ValueError:
            return self.app(env, start_response)
        orig_env = req.environ.copy()
        ctx = Logger499Context(self.app)
        original_resp = ctx.handle_original_call(env, start_response)
        original_resp_status = env['swift.original_status']
        #env['swift.proxy_access_log_made'] = True
        del env['swift.original_status']
        ctx = Logger499Context(self.app)
        return ctx.handle_original_call(orig_env, start_response)

def filter_factory(global_conf, **local_conf):
    conf = global_conf.copy()
    conf.update(local_conf)
    swift_info = {}
    register_swift_info('logger_499', False, **swift_info)

    def logger_499_filter(app):
        return Logger499Middleware(app, conf)
    return logger_499_filter

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
This middleware does very minor things - it copy env to new variable, process the original request, than generate new request based on original env and return response back to the user.
I then activate it by doing GET on existing object

Here is the problem:

If pipeline defined as :

pipeline = .... proxy-logging logger-499 .... proxy-server
Than all works fine and logger prints a single line into proxy-log :

Mar 30 13:47:34 my-laptop proxy-server: 127.0.0.1 127.0.0.1 30/Mar/2014/11/47/34 GET /v1/AUTH_test/contold17031/DSC_0266.JPG HTTP/1.0 200 - - AUTH_tk9331e2ba1b06499e974799f6e6f9a645 - 2730257 -
tx1ffba725a1c347798a2ce-0053380456 - 0.0985 - - 1396180054.443357944 1396180054.541863918

BUT, if I change position of proxy-logging and logger-499, making pipeline to be as
**********************************************************************************************************************
pipeline = .... logger-499 proxy-logging .... proxy-server
Then if I do the same GET i am getting

Mar 30 13:47:34 my-laptop proxy-server: 127.0.0.1 127.0.0.1 30/Mar/2014/11/47/34 GET /v1/AUTH_test/contold17031/DSC_0266.JPG HTTP/1.0 499 - - AUTH_tk9331e2ba1b06499e974799f6e6f9a645 - 65536 - tx1ffba725a1c347798a2ce-0053380456 - 0.0470 - - 1396180054.419362068 1396180054.466345072
Mar 30 13:47:34 my-laptop proxy-server: 127.0.0.1 127.0.0.1 30/Mar/2014/11/47/34 GET /v1/AUTH_test/contold17031/DSC_0266.JPG HTTP/1.0 200 - - AUTH_tk9331e2ba1b06499e974799f6e6f9a645 - 2730257 -
tx1ffba725a1c347798a2ce-0053380456 - 0.0985 - - 1396180054.443357944 1396180054.541863918

To resolve this strange 499 error i need to add
env['swift.proxy_access_log_made'] = True

( see the line #env['swift.proxy_access_log_made'] = True )

Can someone explain me what is wrong with it? Is it something I did wrong or some bug?