Checkbox SRU failed with "ImportError: No module named html"

ubuntu@200908-3521:/tmp$ cat checkbox.log
Traceback (most recent call last):
  File "/usr/bin/checkbox", line 9, in <module>
    load_entry_point('checkbox-ng==0.20.dev', 'console_scripts', 'checkbox')()
  File "/usr/lib/python3/dist-packages/checkbox_ng/main.py", line 41, in main
    raise SystemExit(CheckboxTool().main(argv))
  File "/usr/lib/python3/dist-packages/plainbox/impl/clitools.py", line 310, in main
    self._parser = self.construct_parser(early_ns)
  File "/usr/lib/python3/dist-packages/plainbox/impl/clitools.py", line 469, in construct_parser
    self.add_subcommands(subparsers, early_ns)
  File "/usr/lib/python3/dist-packages/checkbox_ng/tools.py", line 96, in add_subcommands
    from checkbox_ng.commands.launcher import LauncherCommand
  File "/usr/lib/python3/dist-packages/checkbox_ng/commands/launcher.py", line 32, in <module>
    from checkbox_ng.commands.newcli import CliInvocation2
  File "/usr/lib/python3/dist-packages/checkbox_ng/commands/newcli.py", line 42, in <module>
    from plainbox.impl.exporter.html import HTMLSessionStateExporter
ImportError: No module named html

ubuntu@200908-3521:~$ apt-cache policy checkbox
checkbox:
  Installed: 0.17.10+bzr2832+pkg77+legacy1~ubuntu12.04.1
  Candidate: 0.17.10+bzr2832+pkg77+legacy1~ubuntu12.04.1
  Version table:
 *** 0.17.10+bzr2832+pkg77+legacy1~ubuntu12.04.1 0
        500 http://ppa.launchpad.net/checkbox-dev/ppa/ubuntu/ precise/main amd64 Packages
        100 /var/lib/dpkg/status
     0.13.10 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
     0.13.7 0
        500 http://us.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages
        500 http://archive.ubuntu.com/ubuntu/ precise/main amd64 Packages
ubuntu@200908-3521:~$ apt-cache policy plainbox
plainbox:
  Installed: 0.22+bzr3861+pkg31~ubuntu12.04.1
  Candidate: 0.22+bzr3861+pkg31~ubuntu12.04.1
  Version table:
 *** 0.22+bzr3861+pkg31~ubuntu12.04.1 0
        500 http://ppa.launchpad.net/checkbox-dev/ppa/ubuntu/ precise/main amd64 Packages
        100 /var/lib/dpkg/status
ubuntu@200908-3521:~$ plainbox dev list provider
provider '2013.com.canonical.plainbox:manifest'
provider '2013.com.canonical.plainbox:exporters'
provider '2013.com.canonical.plainbox:categories'
provider '2013.com.canonical.certification:certification-client'
provider '2013.com.canonical.certification:checkbox'
provider '2013.com.canonical.certification:plainbox-resources'