QT4 traceback

Exception occurred in traits notification handler for object: <enthought.traits.
ui.ui.UI object at 0x02D4FDE0>, trait: updated, old value: <undefined>, new valu
e: True
Traceback (most recent call last):
  File "C:\Python26\lib\site-packages\traits-3.3.0-py2.6-win32.egg\enthought\tra
its\trait_notifiers.py", line 344, in call_1
    self.handler( object )
  File "C:\Python26\lib\site-packages\traits-3.3.0-py2.6-win32.egg\enthought\tra
its\ui\ui.py", line 877, in _updated_changed
    toolkit().rebuild_ui( self )
  File "C:\Python26\lib\site-packages\traitsbackendqt-3.3.0-py2.6.egg\enthought\
traits\ui\qt4\toolkit.py", line 328, in rebuild_ui
    ui.rebuild( ui, parent )
NameError: global name 'parent' is not defined