UnicodeDecodeError - graph-ancestry crash when generating html

calling "bzr graph-ancestry graph.html" on lp:widelands produces an UnicodeDecodeError
No error if bzr graph-ancestry graph.png is called.

dom 2011-12-04 15:45:52 +0100
0.089 bazaar version: 2.4.2
0.090 bzr arguments: [u'graph-ancestry', u'graph.html']
0.149 looking for plugins in /home/angelo/.bazaar/plugins
0.150 looking for plugins in /usr/lib/pymodules/python2.6/bzrlib/plugins
0.188 looking for plugins in /usr/lib/python2.6/dist-packages/bzrlib/plugins
0.201 encoding stdout as sys.stdout encoding 'UTF-8'
4.547 Transferred: 0kB (0.0kB/s r:0kB w:0kB)
4.551 Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.6/bzrlib/commands.py", line 946, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/pymodules/python2.6/bzrlib/commands.py", line 1150, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/bzrtools/command.py", line 40, in run_argv_aliases
    commands.Command.run_argv_aliases(self, argv, alias_argv)
  File "/usr/lib/pymodules/python2.6/bzrlib/commands.py", line 699, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/pymodules/python2.6/bzrlib/commands.py", line 721, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/pymodules/python2.6/bzrlib/cleanup.py", line 135, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/pymodules/python2.6/bzrlib/cleanup.py", line 165, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/bzrtools/command_classes.py", line 101, in run
    max_distance=max_distance)
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/bzrtools/graph.py", line 415, in write_ancestry_file
    invoke_dot_html(output, filename)
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/bzrtools/dotgraph.py", line 237, in invoke_dot_html
    status = invoke_dot(dot, temp_file, 'cmapx')
  File "/usr/lib/python2.6/dist-packages/bzrlib/plugins/bzrtools/dotgraph.py", line 221, in invoke_dot
    dot_proc.stdin.write(line.encode('utf-8'))
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 29: ordinal not in range(128)

5.329 return code 4