bzr log -rxxx filename crashes

This may or may not be related to bug #300055. The following is a typical error report: This seems to occur only on a 2a format branch. bzr check on the branch shows no errors.

[msapiro@msapiro ...MM_bzr/3.0]$ bzr log -r6790 setup.py
bzr: ERROR: bzrlib.errors.ObjectNotLocked: <bzrlib.groupcompress._GCGraphIndex object at 0x7f8e78cc> is not locked

Traceback (most recent call last):
  File "/usr/lib/python2.6/site-packages/bzrlib/commands.py", line 842, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.6/site-packages/bzrlib/commands.py", line 1037, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.6/site-packages/bzrlib/commands.py", line 654, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.6/site-packages/bzrlib/commands.py", line 1052, in ignore_pipe
    result = func(*args, **kwargs)
  File "/usr/lib/python2.6/site-packages/bzrlib/builtins.py", line 2280, in run
    file_list)
  File "/usr/lib/python2.6/site-packages/bzrlib/log.py", line 1897, in _get_info_for_log_files
    kind = _get_kind_for_file_id(tree, file_id)
  File "/usr/lib/python2.6/site-packages/bzrlib/log.py", line 1929, in _get_kind_for_file_id
    return tree.kind(file_id)
  File "/usr/lib/python2.6/site-packages/bzrlib/revisiontree.py", line 148, in kind
    return self._inventory[file_id].kind
  File "/usr/lib/python2.6/site-packages/bzrlib/inventory.py", line 1883, in __getitem__
    self.id_to_entry.iteritems([(file_id,)]).next()[1])
  File "/usr/lib/python2.6/site-packages/bzrlib/chk_map.py", line 484, in iteritems
    self._ensure_root()
  File "/usr/lib/python2.6/site-packages/bzrlib/chk_map.py", line 138, in _ensure_root
    self._root_node = self._get_node(self._root_node)
  File "/usr/lib/python2.6/site-packages/bzrlib/chk_map.py", line 151, in _get_node
    bytes = self._read_bytes(node)
  File "/usr/lib/python2.6/site-packages/bzrlib/chk_map.py", line 162, in _read_bytes
    bytes = stream.next().get_bytes_as('fulltext')
  File "/usr/lib/python2.6/site-packages/bzrlib/groupcompress.py", line 1423, in get_record_stream
    orig_keys, ordering, include_delta_closure):
  File "/usr/lib/python2.6/site-packages/bzrlib/groupcompress.py", line 1528, in _get_remaining_record_stream
    locations = self._index.get_build_details(keys)
  File "/usr/lib/python2.6/site-packages/bzrlib/groupcompress.py", line 2002, in get_build_details
    self._check_read()
  File "/usr/lib/python2.6/site-packages/bzrlib/groupcompress.py", line 1922, in _check_read
    raise errors.ObjectNotLocked(self)
ObjectNotLocked: <bzrlib.groupcompress._GCGraphIndex object at 0x7f8e78cc> is not locked

bzr 2.0.0 on python 2.6.1 (CYGWIN_NT-5.1-1.5.25-0.156-4-2-i686-32bit-WindowsPE)
arguments: ['/usr/bin/bzr', 'log', '-r6790', 'setup.py']
encoding: 'US-ASCII', fsenc: 'US-ASCII', lang: 'C'
plugins:
  bzrtools /usr/lib/python2.6/site-packages/bzrlib/plugins/bzrtools [2.0.1]
  launchpad /usr/lib/python2.6/site-packages/bzrlib/plugins/launchpad [2.0.0]
  netrc_credential_store /usr/lib/python2.6/site-packages/bzrlib/plugins/netrc_credential_store [2.0.0]

*** 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.
[msapiro@msapiro ...MM_bzr/3.0]$