Tools \ Add Tool dialog generates TypeError

[BE 0.10.0dev, r340 - on WinXP]

From BE main window, select Tools, then Add Tool.

bzr: ERROR: exceptions.TypeError: argument 2 of QComboBox.addItem() has an invalid type

Traceback (most recent call last):
  File "C:/localapp/Program Files/Bazaar/plugins\explorer\lib\explorer.py", line 1595, in do_add_tool
  File "C:/localapp/Program Files/Bazaar/plugins\explorer\lib\tool_dialogs.py", line 28, in __init__
  File "C:/localapp/Program Files/Bazaar/plugins\explorer\lib\tool_dialogs.py", line 36, in _build_layout
  File "C:/localapp/Program Files/Bazaar/plugins\explorer\lib\tool_dialogs.py", line 64, in _build_combo_with_labels
TypeError: argument 2 of QComboBox.addItem() has an invalid type

bzr 2.1.0b3 on python 2.5.4 (win32)
arguments: ['C:\\localapp\\Program Files\\Bazaar\\bzr.exe', 'explorer']
encoding: 'cp1252', fsenc: 'mbcs', lang: None
plugins:
  bzrtools C:\localapp\Program Files\Bazaar\plugins\bzrtools [2.1.0b1]
  explorer C:\localapp\Program Files\Bazaar\plugins\explorer [0.10.0dev]
  extmerge C:\localapp\Program Files\Bazaar\plugins\extmerge [unknown]
  launchpad C:\localapp\Program Files\Bazaar\plugins\launchpad [2.1.0b3]
  netrc_credential_store C:\localapp\Program Files\Bazaar\plugins\netrc_credential_store [2.1.0b3]
  qbzr C:\localapp\Program Files\Bazaar\plugins\qbzr [0.17.0dev]
  rebase C:\localapp\Program Files\Bazaar\plugins\rebase [0.5.4]
  svn C:\localapp\Program Files\Bazaar\plugins\svn [1.0.1]
  upload C:\localapp\Program Files\Bazaar\plugins\upload [1.0.0dev]
  xmloutput C:\localapp\Program Files\Bazaar\plugins\xmloutput [0.8.5]