UnicodeDecodeError on Vivid for non-ascii characters in config files

Upgraded to Vivid, my bazaar.conf contains the letter "é".
Most bzr commands now fail with UnicodeDecodeError in bzrlib/rio.py

bzr 2.7.0dev1 on python 2.7.8 (Linux-3.16.0-24-generic-x86_64-with-
    Ubuntu-15.04-vivid)
arguments: ['/usr/bin/bzr', 'init']
plugins: bash_completion[2.7.0dev1], builddeb[2.8.6],
    changelog_merge[2.7.0dev1], grep[2.7.0dev1], launchpad[2.7.0dev1],
    netrc_credential_store[2.7.0dev1], news_merge[2.7.0dev1],
    po_merge[2.7.0dev1], weave_fmt[2.7.0dev1]
encoding: 'utf-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'

bzr: ERROR: exceptions.UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 10: ordinal not in range(128)

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/builtins.py", line 2116, in run
    force_new_tree=force_new_tree)
  File "/usr/lib/python2.7/dist-packages/bzrlib/controldir.py", line 642, in create_branch_convenience
    controldir = klass.create(base, format, possible_transports)
  File "/usr/lib/python2.7/dist-packages/bzrlib/controldir.py", line 840, in create
    return format.initialize_on_transport(t)
  File "/usr/lib/python2.7/dist-packages/bzrlib/bzrdir.py", line 1321, in initialize_on_transport
    return self._initialize_on_transport_vfs(transport)
  File "/usr/lib/python2.7/dist-packages/bzrlib/bzrdir.py", line 1463, in _initialize_on_transport_vfs
    control_files.lock_write()
  File "/usr/lib/python2.7/dist-packages/bzrlib/lockable_files.py", line 164, in lock_write
    token_from_lock = self._lock.lock_write(token=token)
  File "/usr/lib/python2.7/dist-packages/bzrlib/lockdir.py", line 674, in lock_write
    return self.wait_lock()
  File "/usr/lib/python2.7/dist-packages/bzrlib/lockdir.py", line 603, in wait_lock
    return self.attempt_lock()
  File "/usr/lib/python2.7/dist-packages/bzrlib/lockdir.py", line 552, in attempt_lock
    result = self._attempt_lock()
  File "/usr/lib/python2.7/dist-packages/bzrlib/lockdir.py", line 238, in _attempt_lock
    tmpname = self._create_pending_dir()
  File "/usr/lib/python2.7/dist-packages/bzrlib/lockdir.py", line 342, in _create_pending_dir
    info.to_bytes())
  File "/usr/lib/python2.7/dist-packages/bzrlib/lockdir.py", line 786, in to_bytes
    s = rio.Stanza(**self.info_dict)
  File "/usr/lib/python2.7/dist-packages/bzrlib/rio.py", line 118, in __init__
    self.add(tag, value)
  File "/usr/lib/python2.7/dist-packages/bzrlib/rio.py", line 125, in add
    value = unicode(value)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 10: ordinal not in range(128)

bzr 2.7.0dev1 on python 2.7.8 (Linux-3.16.0-24-generic-x86_64-with-
    Ubuntu-15.04-vivid)
arguments: ['/usr/bin/bzr', 'init']
plugins: bash_completion[2.7.0dev1], builddeb[2.8.6],
    changelog_merge[2.7.0dev1], grep[2.7.0dev1], launchpad[2.7.0dev1],
    netrc_credential_store[2.7.0dev1], news_merge[2.7.0dev1],
    po_merge[2.7.0dev1], weave_fmt[2.7.0dev1]
encoding: 'utf-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'

*** 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.