git clone bzr::lp:byobu crashes with AssertionError

When attempting to clone lp:byobu (git clone bzr::lp:byobu), it crashes with an AssertionError.

Traceback (most recent call last):
  File "/usr/bin/git-remote-bzr", line 49, in <module>
    helper.process(sys.stdin, sys.stdout)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/git_remote_helper.py", line 171, in process
    self.process_line(l, outf)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/git_remote_helper.py", line 187, in process_line
    self.commands[argv[0]](self, outf, argv)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/git_remote_helper.py", line 120, in cmd_list
    for ref, git_sha1 in refs.as_dict().iteritems():
  File "/usr/lib/python2.7/dist-packages/dulwich/repo.py", line 202, in as_dict
    ret[key] = self[("%s/%s" % (base, key)).strip("/")]
  File "/usr/lib/python2.7/dist-packages/dulwich/repo.py", line 273, in __getitem__
    _, sha = self._follow(name)
  File "/usr/lib/python2.7/dist-packages/dulwich/repo.py", line 255, in _follow
    contents = self.read_ref(refname)
  File "/usr/lib/python2.7/dist-packages/dulwich/repo.py", line 231, in read_ref
    contents = self.read_loose_ref(refname)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/refs.py", line 136, in read_loose_ref
    return self.object_store._lookup_revision_sha1(revid)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/object_store.py", line 580, in _lookup_revision_sha1
    self._update_sha_map(revid)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/object_store.py", line 384, in _update_sha_map
    self._update_sha_map_revision(revid)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/object_store.py", line 484, in _update_sha_map_revision
    for path, obj, ie in self._revision_to_objects(rev, tree, lossy=(not self.mapping.roundtripping)):
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/object_store.py", line 451, in _revision_to_objects
    root_tree = self[self[base_sha1].tree]
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/object_store.py", line 692, in __getitem__
    tree, unusual_modes, expected_sha=sha)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/object_store.py", line 559, in _reconstruct_tree
    _check_expected_sha(expected_sha, tree)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/git/object_store.py", line 154, in _check_expected_sha
    expected_sha))
AssertionError: Invalid sha for <Tree e0fbef63463fb9b7ad89b4c3f022ef85aa070625>: edbe1548737e4471013d4b8d218dd33867589577

bzr-git version is 0.6.9-1.