branching from Hg: "Unknown VCS 'svn-v3-none'"

[ChriS]

bzr branch https://forge.ocamlcore.org/anonscm/hg/tuareg/trunk

raises an exception :
bzr: ERROR: exceptions.KeyError: "Unknown VCS 'svn-v3-none'"

Traceback (most recent call last):
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 926, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 1126, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 691, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.6/dist-packages/bzrlib/commands.py", line 713, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/cleanup.py", line 135, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/cleanup.py", line 165, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/builtins.py", line 1227, in run
    source_branch=br_from)
  File "/usr/lib/python2.6/dist-packages/bzrlib/controldir.py", line 374, in sprout
    create_tree_if_local=create_tree_if_local)
  File "/usr/lib/python2.6/dist-packages/bzrlib/cleanup.py", line 131, in run
    self.cleanups, self.func, self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/cleanup.py", line 165, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/controldir.py", line 427, in _sprout
    result_repo.fetch(source_repository, fetch_spec=fetch_spec)
  File "/usr/lib/python2.6/dist-packages/bzrlib/repository.py", line 1781, in fetch
    find_ghosts=find_ghosts, fetch_spec=fetch_spec)
  File "/usr/lib/python2.6/dist-packages/bzrlib/decorators.py", line 194, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/hg/fetch.py", line 710, in fetch
    self.addchangegroup(cg, mapping)
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/hg/fetch.py", line 566, in addchangegroup
    self._unpack_changesets(changesetchunks, mapping, pb)
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/hg/fetch.py", line 454, in _unpack_changesets
    manifest, user, (time, timezone), desc, extra)
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/hg/mapping.py", line 360, in import_revision
    result.properties['converted-from'] = convert_converted_from(value)
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/hg/mapping.py", line 59, in convert_converted_from
    raise KeyError("Unknown VCS '%s'" % kind)
KeyError: "Unknown VCS 'svn-v3-none'"

bzr 2.3.1 on python 2.6.6 (Linux-2.6.38.2-x86_64-with-debian-wheezy-sid)
arguments: ['/usr/bin/bzr', 'branch', 'https://forge.ocamlcore.org/anonscm/hg/tuareg/trunk']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'
plugins:
  bash_completion /usr/lib/python2.6/dist-packages/bzrlib/plugins/bash_completion [2.3.1]
  bzrtools /usr/lib/python2.6/dist-packages/bzrlib/plugins/bzrtools [2.3.1]
  dbus /usr/lib/python2.6/dist-packages/bzrlib/plugins/dbus [0.1.0dev]
  explorer /usr/lib/python2.6/dist-packages/bzrlib/plugins/explorer [1.1.2]
  fastimport /usr/lib/python2.6/dist-packages/bzrlib/plugins/fastimport [0.11.0dev]
  git /usr/lib/python2.6/dist-packages/bzrlib/plugins/git [0.6.0]
  gtk /usr/lib/python2.6/dist-packages/bzrlib/plugins/gtk [0.101.0dev]
  hg /usr/lib/python2.6/dist-packages/bzrlib/plugins/hg [0.2.0dev]
  launchpad /usr/lib/python2.6/dist-packages/bzrlib/plugins/launchpad [2.3.1]
  netrc_credential_store /usr/lib/python2.6/dist-packages/bzrlib/plugins/netrc_credential_store [2.3.1]
  news_merge /usr/lib/python2.6/dist-packages/bzrlib/plugins/news_merge [2.3.1]
  qbzr /usr/lib/python2.6/dist-packages/bzrlib/plugins/qbzr [0.20.0]
  stats /usr/lib/python2.6/dist-packages/bzrlib/plugins/stats [0.1.0]
  svn /usr/lib/python2.6/dist-packages/bzrlib/plugins/svn [1.0.5dev]