bzr serve from 1.2 server to 1.5 client fails on client side

[David Ingamells]

I have a bazaar serve running on one machine using bzr version 1.2. On 
another machine with bzr v1.5 I try

bzr log bzr://x/y

and get a traceback. Are there known problems with such a combination?
I've tried 1.2 to 1.2 and 1.5 to 1.5 and it works fine.

David.

here is the traceback:

bzr: ERROR: exceptions.ValueError: key None not a plain string

Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 846, 
in run_bzr_catch_errors
    return run_bzr(argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 797, 
in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 499, 
in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 807, 
in ignore_pipe
    result = func(*args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/builtins.py", line 1774, 
in run
    limit=limit)
  File "/usr/lib/python2.5/site-packages/bzrlib/log.py", line 185, in 
show_log
    start_revision, end_revision, search, limit)
  File "/usr/lib/python2.5/site-packages/bzrlib/log.py", line 215, in 
_show_log
    allow_single_merge_revision)
  File "/usr/lib/python2.5/site-packages/bzrlib/log.py", line 273, in 
calculate_view_revisions
    view_revisions = _filter_revision_range(list(view_revs_iter),
  File "/usr/lib/python2.5/site-packages/bzrlib/log.py", line 526, in 
get_view_revisions
    graph.iter_ancestry(mainline_revs) if value is not None))
  File "/usr/lib/python2.5/site-packages/bzrlib/log.py", line 525, in 
<genexpr>
    parent_map = dict(((key, value) for key, value in
  File "/usr/lib/python2.5/site-packages/bzrlib/graph.py", line 623, in 
iter_ancestry
    next_map = self.get_parent_map(pending)
  File "/usr/lib/python2.5/site-packages/bzrlib/remote.py", line 812, in 
get_parent_map
    parent_map = self._get_parent_map(missing_revisions)
  File "/usr/lib/python2.5/site-packages/bzrlib/remote.py", line 888, in 
_get_parent_map
    "key %r not a plain string" % (key,))
ValueError: key None not a plain string

bzr 1.5 on python 2.5.1 (linux2)
arguments: ['/usr/bin/bzr', 'log', 'bzr://mscvs01/CVTOOL/Sting_1.0']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_GB.UTF-8'
plugins:
  bzrtools             
/usr/lib/python2.5/site-packages/bzrlib/plugins/bzrtools [1.5.0]
  gtk                  
/usr/lib/python2.5/site-packages/bzrlib/plugins/gtk [0.93.0]
  launchpad            
/usr/lib/python2.5/site-packages/bzrlib/plugins/launchpad [unknown]
*** Bazaar has encountered an internal error.
    Please report a bug at https://bugs.launchpad.net/bzr/+filebug
    including this traceback, and a description of what you
    were doing when the error occurred.