ObjectNotLocked doing 'bzr log -r 199 path/to/file'

This can be seen with a branch of bzr in 2a format:

$ bzr log -r 199 NEWS
bzr: ERROR: bzrlib.errors.ObjectNotLocked: <bzrlib.groupcompress._GCGraphIndex object at 0xa2e6a4c> is not locked

Traceback (most recent call last):
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 842, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 1037, in run_bzr
    ret = run(*run_argv)
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 654, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 1052, in ignore_pipe
    result = func(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/builtins.py", line 2278, in run
    file_list)
  File "/home/andrew/code/bzr/bzrlib/log.py", line 1897, in _get_info_for_log_files
    kind = _get_kind_for_file_id(tree, file_id)
  File "/home/andrew/code/bzr/bzrlib/log.py", line 1929, in _get_kind_for_file_id
    return tree.kind(file_id)
  File "/home/andrew/code/bzr/bzrlib/revisiontree.py", line 148, in kind
    return self._inventory[file_id].kind
  File "/home/andrew/code/bzr/bzrlib/inventory.py", line 2008, in __getitem__
    self.id_to_entry.iteritems([(file_id,)]).next()[1])
  File "/home/andrew/code/bzr/bzrlib/chk_map.py", line 484, in iteritems
    self._ensure_root()
  File "/home/andrew/code/bzr/bzrlib/chk_map.py", line 138, in _ensure_root
    self._root_node = self._get_node(self._root_node)
  File "/home/andrew/code/bzr/bzrlib/chk_map.py", line 151, in _get_node
    bytes = self._read_bytes(node)
  File "/home/andrew/code/bzr/bzrlib/chk_map.py", line 162, in _read_bytes
    bytes = stream.next().get_bytes_as('fulltext')
  File "/home/andrew/code/bzr/bzrlib/groupcompress.py", line 1423, in get_record_stream
    orig_keys, ordering, include_delta_closure):
  File "/home/andrew/code/bzr/bzrlib/groupcompress.py", line 1528, in _get_remaining_record_stream
    locations = self._index.get_build_details(keys)
  File "/home/andrew/code/bzr/bzrlib/groupcompress.py", line 2002, in get_build_details
    self._check_read()
  File "/home/andrew/code/bzr/bzrlib/groupcompress.py", line 1922, in _check_read
    raise errors.ObjectNotLocked(self)
ObjectNotLocked: <bzrlib.groupcompress._GCGraphIndex object at 0xa2e6a4c> is not locked

bzr 2.1.0dev on python 2.6.2 (Linux-2.6.28-15-generic-i686-with-Ubuntu-9.04-jaunty)
arguments: ['/home/andrew/code/bzr/bzr', '-Dhpss', 'log', '-r', '199', 'NEWS']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_AU.UTF-8'
plugins:
  bisect /home/andrew/.bazaar/plugins/bisect [1.1.0.pre.0]
  bzrtools /home/andrew/.bazaar/plugins/bzrtools [2.0.0]
  ec2test /home/andrew/.bazaar/plugins/ec2test [unknown]
  extmerge /home/andrew/.bazaar/plugins/extmerge [unknown]
  gtk /home/andrew/.bazaar/plugins/gtk [0.98.0dev1]
  launchpad /home/andrew/code/bzr/bzrlib/plugins/launchpad [2.1.0dev]
  loom /home/andrew/.bazaar/plugins/loom [1.4.0dev]
  melddiff /home/andrew/.bazaar/plugins/melddiff [unknown]
  netrc_credential_store /home/andrew/code/bzr/bzrlib/plugins/netrc_credential_store [2.1.0dev]
  ping /home/andrew/.bazaar/plugins/ping [unknown]
  pqm /home/andrew/.bazaar/plugins/pqm [1.3.0dev]
  push_and_update /home/andrew/.bazaar/plugins/push_and_update [unknown]
  qbzr /home/andrew/.bazaar/plugins/qbzr [0.15.0dev]
  rebase /home/andrew/.bazaar/plugins/rebase [0.5.2dev]
  removable /home/andrew/.bazaar/plugins/removable [unknown]
  repokeys /home/andrew/.bazaar/plugins/repokeys [unknown]
  stats /home/andrew/.bazaar/plugins/stats [unknown]
  subunit_selftest /home/andrew/.bazaar/plugins/subunit_selftest.py [unknown]
  svn /home/andrew/.bazaar/plugins/svn [1.0.0dev]
  usertest /home/andrew/.bazaar/plugins/usertest [unknown]

*** Bazaar has encountered an internal error. This probably indicates a
    bug in Bazaar. You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/bzr/+filebug
    including this traceback and a description of the problem.

Presumably there's a missing lock_read somewhere.

This was originally reported in <https://bugs.edge.launchpad.net/bzr/+bug/389413/comments/5>, but turns out to be a separate bug to bug 389413.