Bug#681598: /usr/share/pyshared/lsb_release.py: release detection fails with http.debian.net redirector in sources.list

Package: lsb-release
Version: 4.1+Debian7
Severity: normal
File: /usr/share/pyshared/lsb_release.py

With the following sources.list:

| deb-src http://mirror.cc.columbia.edu/debian/ testing main contrib non-free
| deb http://mirror.cc.columbia.edu/debian/ testing main contrib non-free

the output of lsb_release.get_distro_information is correct:

In [4]: lsb_release.get_distro_information()
Out[4]: 
{'CODENAME': 'wheezy',
 'DESCRIPTION': u'Debian GNU/Linux testing (wheezy)',
 'ID': 'Debian',
 'OS': 'GNU/Linux',
 'RELEASE': u'testing'}


When using the http.debian.net redirector, though

| deb-src http://http.debian.net/debian/ testing main contrib non-free
| deb http://http.debian.net/debian/ testing main contrib non-free

the detection fails:

In [3]: lsb_release.parse_apt_policy()
Out[3]: 
[(100, {'suite': u'now'}),
 (500,
  {'component': u'',
   'label': u'Jitsi Debian packages repository',
   'origin': u'jitsi.org',
   'suite': u'unstable'}),
 (100,
  {'component': u'non-free',
   'label': u'Unofficial Multimedia Packages',
   'origin': u'Unofficial Multimedia Packages',
   'suite': u'testing',
   'version': u'None'}),
 (100,
  {'component': u'main',
   'label': u'Unofficial Multimedia Packages',
   'origin': u'Unofficial Multimedia Packages',
   'suite': u'testing',
   'version': u'None'}),
 (500,
  {'component': u'non-free',
   'label': u'Debian',
   'origin': u'Debian',
   'suite': u'testing'}),
 (500,
  {'component': u'contrib',
   'label': u'Debian',
   'origin': u'Debian',
   'suite': u'testing'}),
 (500,
  {'component': u'main',
   'label': u'Debian',
   'origin': u'Debian',
   'suite': u'testing'})]


This is annoying, because when using ${distro_codename} in /etc/apt/apt.conf.d/50unattended-upgrades, 

Unattended-Upgrade::Origins-Pattern {
        "o={distro_id},a=${distro_codename}";
        "o={distro_id},a=${distro_codename}-updates";
        "o={distro_id},a=${distro_codename},l=Debian-Security";
};


unattended-upgrades fails with

Traceback (most recent call last):
  File "/usr/bin/unattended-upgrade", line 55, in <module>
    DISTRO_CODENAME = lsb_release.get_distro_information()['CODENAME']
KeyError: 'CODENAME'




-- Package-specific info:
lsb_release output
-*- -*- -*- -*- -*-
Distributor ID:	Debian
Description:	Debian GNU/Linux testing (wheezy)
Release:	testing
Codename:	wheezy
-*- -*- -*- -*- -*-
    Apt policy
-*- -*- -*- -*- -*-
Package files:
 100 /var/lib/dpkg/status
     release a=now
 500 http://download.jitsi.org/deb/ unstable/ Packages
     release o=jitsi.org,a=unstable,n=sid,l=Jitsi Debian packages repository,c=
     origin download.jitsi.org
 100 http://www.debian-multimedia.org/ testing/non-free amd64 Packages
     release v=None,o=Unofficial Multimedia Packages,a=testing,n=wheezy,l=Unofficial Multimedia Packages,c=non-free
     origin www.debian-multimedia.org
 100 http://www.debian-multimedia.org/ testing/main amd64 Packages
     release v=None,o=Unofficial Multimedia Packages,a=testing,n=wheezy,l=Unofficial Multimedia Packages,c=main
     origin www.debian-multimedia.org
 500 http://mirror.cc.columbia.edu/debian/ testing/non-free Translation-en
 500 http://mirror.cc.columbia.edu/debian/ testing/main Translation-en
 500 http://mirror.cc.columbia.edu/debian/ testing/contrib Translation-en
 500 http://mirror.cc.columbia.edu/debian/ testing/non-free amd64 Packages
     release o=Debian,a=testing,n=wheezy,l=Debian,c=non-free
     origin mirror.cc.columbia.edu
 500 http://mirror.cc.columbia.edu/debian/ testing/contrib amd64 Packages
     release o=Debian,a=testing,n=wheezy,l=Debian,c=contrib
     origin mirror.cc.columbia.edu
 500 http://mirror.cc.columbia.edu/debian/ testing/main amd64 Packages
     release o=Debian,a=testing,n=wheezy,l=Debian,c=main
     origin mirror.cc.columbia.edu
Pinned packages:
-*- -*- -*- -*- -*-
   sources.list
-*- -*- -*- -*- -*-
deb-src http://mirror.cc.columbia.edu/debian/ testing main contrib non-free
deb http://mirror.cc.columbia.edu/debian/ testing main contrib non-free
deb http://www.debian-multimedia.org testing main non-free
-*- -*- -*- -*- -*-
 /etc/lsb_release
-*- -*- -*- -*- -*-
- none

-- System Information:
Debian Release: wheezy/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 3.2.0-3-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages lsb-release depends on:
ii  python     2.7.3~rc2-1
ii  python2.6  2.6.8-0.2
ii  python2.7  2.7.3~rc2-2.1

Versions of packages lsb-release recommends:
ii  apt  0.9.7.1

Versions of packages lsb-release suggests:
pn  lsb  <none>

-- no debconf information