"bzr status" errors

ABSTRACT:
Using "bzr status" leads to errors

STEPS TO REPRODUCE:
1. Run "bzr status" from the command line

RESULT:
I get some status result, followed by what looks like a serious error message:

bzr: ERROR: exceptions.KeyError: 'pop(): dictionary is empty'

Traceback (most recent call last):
  File "/Library/Python/2.5/site-packages/bzrlib/commands.py", line 846, in run_bzr_catch_errors
    return run_bzr(argv)
  File "/Library/Python/2.5/site-packages/bzrlib/commands.py", line 797, in run_bzr
    ret = run(*run_argv)
  File "/Library/Python/2.5/site-packages/bzrlib/commands.py", line 499, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/Library/Python/2.5/site-packages/bzrlib/commands.py", line 807, in ignore_pipe
    result = func(*args, **kwargs)
  File "/Library/Python/2.5/site-packages/bzrlib/builtins.py", line 178, in run
    show_pending=not no_pending)
  File "/Library/Python/2.5/site-packages/bzrlib/status.py", line 142, in show_tree_status
    show_pending_merges(new, to_file, short)
  File "/Library/Python/2.5/site-packages/bzrlib/status.py", line 235, in show_pending_merges
    branch.repository.get_parent_map(merge_extra))
  File "/Library/Python/2.5/site-packages/bzrlib/status.py", line 172, in _get_sorted_revisions
    sorter = tsort.MergeSorter(parent_graph, tip_revision)
  File "/Library/Python/2.5/site-packages/bzrlib/tsort.py", line 412, in __init__
    parents = self._graph.pop(branch_tip)
KeyError: 'pop(): dictionary is empty'

bzr 1.5 on python 2.5.1 (darwin)
arguments: ['/usr/local/bin/bzr', 'status']
encoding: 'UTF-8', fsenc: 'utf-8', lang: 'en_US.UTF-8'
plugins:
  bzrtools /Library/Python/2.5/site-packages/bzrlib/plugins/bzrtools [1.5.0]
  launchpad /Library/Python/2.5/site-packages/bzrlib/plugins/launchpad [unknown]
  qbzr /Library/Python/2.5/site-packages/bzrlib/plugins/qbzr [0.9.0]
  rebase /Library/Python/2.5/site-packages/bzrlib/plugins/rebase [0.3.0dev0]
*** 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.

NOTES:
This happens consistently.
Running MacOSX 10.5.4 on a Powerbook G4.