bzr log crashes with match pattern

run `bzr log --match="some_string"` causes the following error

    bzr: ERROR: exceptions.TypeError: expected string or buffer

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 930, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 1121, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 673, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 697, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 136, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 1138, in ignore_pipe
    result = func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/builtins.py", line 2893, in run
    Logger(b, rqst).show(lf)
  File "/usr/lib/python2.7/dist-packages/bzrlib/log.py", line 382, in show
    self._show_body(lf)
  File "/usr/lib/python2.7/dist-packages/bzrlib/log.py", line 411, in _show_body
    for lr in generator.iter_log_revisions():
  File "/usr/lib/python2.7/dist-packages/bzrlib/log.py", line 451, in iter_log_revisions
    for revs in revision_iterator:
  File "/usr/lib/python2.7/dist-packages/bzrlib/log.py", line 872, in _filter_re
    new_revs = [rev for rev in revs if _match_filter(searchRE, rev[1])]
  File "/usr/lib/python2.7/dist-packages/bzrlib/log.py", line 886, in _match_filter
    if k in strings and not _match_any_filter(strings[k], v):
  File "/usr/lib/python2.7/dist-packages/bzrlib/log.py", line 891, in _match_any_filter
    return any([filter(None, map(re.search, strings)) for re in res])
TypeError: expected string or buffer

bzr 2.7.0dev1 on python 2.7.6 (Linux-3.13.0-66-generic-x86_64-with-
    Ubuntu-14.04-trusty)
arguments: ['/usr/bin/bzr', 'log', '-m', 'drizzle_con_st']
plugins: bash_completion[2.7.0dev1], bzrtools[2.6.0],
    changelog_merge[2.7.0dev1], explorer[1.3.0], fastimport[0.13.0],
    grep[2.7.0dev1], launchpad[2.7.0dev1], netrc_credential_store[2.7.0dev1],
    news_merge[2.7.0dev1], po_merge[2.7.0dev1], qbzr[0.23.1],
    weave_fmt[2.7.0dev1]
encoding: 'utf-8', fsenc: 'UTF-8', lang: 'en_GB.UTF-8'