bisect fails, attempting to add a revision twice

Here is a traceback. This eventually happens on every non-trivial bisect I have attempted to perform on a particular internal project. Unfortunately I have not been able to distill a simple test case.

bzr: ERROR: exceptions.RuntimeError: attempting to add revid <email address hidden> twice

Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 893, in run_bzr_catch_errors
    return run_bzr(argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 839, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 539, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/home/mental/.bazaar/plugins/bisect/__init__.py", line 349, in run
    self.yes(revision)
  File "/home/mental/.bazaar/plugins/bisect/__init__.py", line 387, in yes
    self._set_state(revspec, "yes")
  File "/home/mental/.bazaar/plugins/bisect/__init__.py", line 325, in _set_state
    bisect_log.set_current(state)
  File "/home/mental/.bazaar/plugins/bisect/__init__.py", line 237, in set_current
    self._set_status(self._current.get_current_revid(), status)
  File "/home/mental/.bazaar/plugins/bisect/__init__.py", line 203, in _set_status
    raise RuntimeError("attempting to add revid %s twice" % revid)
RuntimeError: attempting to add revid <email address hidden> twice

bzr 1.9 on python 2.5.2 (linux2)
arguments: ['/usr/bin/bzr', 'bisect', 'yes']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_US.UTF-8'
plugins:
  bisect /home/mental/.bazaar/plugins/bisect [1.1.0pre0]
  bzrtools /usr/lib/python2.5/site-packages/bzrlib/plugins/bzrtools [1.9.1]
  launchpad /usr/lib/python2.5/site-packages/bzrlib/plugins/launchpad [unknown]
  pqm /home/mental/.bazaar/plugins/pqm [1.4.0dev0]
  rebase /home/mental/.bazaar/plugins/rebase [0.4.3dev0]
  stats /home/mental/.bazaar/plugins/stats [unknown]