Comment 7 for bug 496879

The reason of the bug is that :
1. In softwareproperties/SoftwareProperties.py, a thread is created

  def check_and_add_key_for_whitelisted_channels(self, srcline):
[...]
    if parsed_uri.netloc == 'ppa.launchpad.net':
      worker = AddPPASigningKeyThread(parsed_uri.path)
      worker.start()

2. When failing in method add_ppa_signing_key of AddPPASigningKeyThread class, it prints an error and return False :
[...]
        except URLError, e:
            print "Error reading %s: %s" % (lp_url, e)
            return False

3. But the return code generated by the thread is nowhere managed. In fact, two lines are inconditionnaly added in source file :
  def add_source_from_line(self, line):
[...]
    self.check_and_add_key_for_whitelisted_channels(deb_line)
    self.sourceslist.list.append(new_deb_entry)
    self.sourceslist.list.append(new_debsrc_entry)

Hope it helps...