update fails when trying to lock master branch (in a readonly checkout)

Checkouts seem to randomly break and refuse to update (ie. 'bzr update') with "bzr: ERROR: Cannot lock LockDir(lp-45197200:///~oem-solutions-releng/bugsy/lexbuild-production-projectconfig/.bzr/branchlock): Transport operation not possible: readonly transport". This has happened a number of times on different machines running bzr 1.17. Unbinding and then rebinding the branch seems to fix the issue.

Wed 2009-08-12 14:08:28 -0400
0.688 bzr arguments: [u'update']
0.914 looking for plugins in /home/lexbuilder/.bazaar/plugins
0.915 looking for plugins in /usr/lib/python2.5/site-packages/bzrlib/plugins
2.118 encoding stdout as sys.stdout encoding 'ANSI_X3.4-1968'
3.079 opening working tree '/var/tmp/lexbuild-projects/lexbuild-production-projectconfig'
3.545 ssh implementation is OpenSSH
14.462 Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 835, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 1030, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 647, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.5/site-packages/bzrlib/builtins.py", line 1409, in run
    view_info=view_info), possible_transports=possible_transports)
  File "/usr/lib/python2.5/site-packages/bzrlib/workingtree.py", line 2190, in update
    old_tip = self.branch.update(possible_transports)
  File "/usr/lib/python2.5/site-packages/bzrlib/decorators.py", line 192, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 2396, in update
    self.pull(master, overwrite=True)
  File "/usr/lib/python2.5/site-packages/bzrlib/decorators.py", line 192, in write_locked
    result = unbound(self, *args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 891, in pull
    possible_transports=possible_transports, *args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/branch.py", line 3145, in pull
    master_branch.lock_write()
  File "/usr/lib/python2.5/site-packages/bzrlib/remote.py", line 2178, in lock_write
    remote_tokens = self._remote_lock_write(token)
  File "/usr/lib/python2.5/site-packages/bzrlib/remote.py", line 2169, in _remote_lock_write
    repo_token or '', **err_context)
  File "/usr/lib/python2.5/site-packages/bzrlib/remote.py", line 54, in _call
    return self._client.call(method, *args)
  File "/usr/lib/python2.5/site-packages/bzrlib/smart/client.py", line 129, in call
    result, protocol = self.call_expecting_body(method, *args)
  File "/usr/lib/python2.5/site-packages/bzrlib/smart/client.py", line 142, in call_expecting_body
    method, args, expect_response_body=True)
  File "/usr/lib/python2.5/site-packages/bzrlib/smart/client.py", line 78, in _call_and_read_response
    expect_body=expect_response_body),
  File "/usr/lib/python2.5/site-packages/bzrlib/smart/message.py", line 306, in read_response_tuple
    _translate_error(self.args)
  File "/usr/lib/python2.5/site-packages/bzrlib/smart/message.py", line 355, in _translate_error
    raise errors.LockFailed(*error_args[:2])
LockFailed: Cannot lock LockDir(lp-45197200:///~oem-solutions-releng/bugsy/lexbuild-production-projectconfig/.bzr/branchlock): Transport operation not possible: readonly transport

Wed 2009-08-12 14:16:22 -0400
0.079 bzr arguments: [u'unbind']
0.095 looking for plugins in /home/lexbuilder/.bazaar/plugins
0.095 looking for plugins in /usr/lib/python2.5/site-packages/bzrlib/plugins
0.329 encoding stdout as sys.stdout encoding 'ANSI_X3.4-1968'
1.107 return code 0

Wed 2009-08-12 14:16:25 -0400
0.026 bzr arguments: [u'bind']
0.043 looking for plugins in /home/lexbuilder/.bazaar/plugins
0.043 looking for plugins in /usr/lib/python2.5/site-packages/bzrlib/plugins
0.108 encoding stdout as sys.stdout encoding 'ANSI_X3.4-1968'
0.524 ssh implementation is OpenSSH
4.521 return code 0

Wed 2009-08-12 14:16:32 -0400
0.018 bzr arguments: [u'update']
0.034 looking for plugins in /home/lexbuilder/.bazaar/plugins
0.034 looking for plugins in /usr/lib/python2.5/site-packages/bzrlib/plugins
0.165 encoding stdout as sys.stdout encoding 'ANSI_X3.4-1968'
0.500 opening working tree '/var/tmp/lexbuild-projects/lexbuild-production-projectconfig'
0.574 ssh implementation is OpenSSH
5.374 Using fetch logic to copy between RemoteRepository(bzr+ssh://bazaar.launchpad.net/~oem-solutions-releng/bugsy/lexbuild-production-projectconfig/.bzr/)(<RemoteRepositoryFormat>) and KnitPackRepository('file:///var/tmp/lexbuild-projects/lexbuild-production-projectconfig/.bzr/repository/')(<RepositoryFormatKnitPack1>)
5.374 fetch up to rev {<email address hidden>}
[25720] 2009-08-12 14:16:40.032 INFO: +N athens/binary_local-includes/install/
[25720] 2009-08-12 14:16:40.033 INFO: +N athens/binary_local-includes/install/recipe
[25720] 2009-08-12 14:16:40.033 INFO: +N athens/chroot_local-packageslists/kidsafe
[25720] 2009-08-12 14:16:40.033 INFO: +N athens/chroot_local-packageslists/language-support-el
[25720] 2009-08-12 14:16:40.034 INFO: M athens/binary_debian-installer/preseed.cfg
[25720] 2009-08-12 14:16:40.034 INFO: M athens/chroot
[25720] 2009-08-12 14:16:40.034 INFO: -D athens/chroot_local-hooks/generate-firstboot-oemconfig-archive.sh
[25720] 2009-08-12 14:16:40.034 INFO: M chelsea-big/project
[25720] 2009-08-12 14:16:40.035 INFO: M cody/binary_local-udebs/recovery-installer_0.1_all.udeb
[25720] 2009-08-12 14:16:40.083 INFO: All changes applied successfully.
[25720] 2009-08-12 14:16:40.109 INFO: Updated to revision 677.
7.868 return code 0