From the Orca list:

On Sun, 2010-05-16 at 13:49 -0300, jose vilmar estacio de souza wrote:
> Hi all.
> I don't no how, I don't why but I found the following messages in debug 
> output from orca.
> 
> vvvvv PROCESS OBJECT EVENT object:state-changed:focused vvvvv
> OBJECT EVENT: object:state-changed:focused             detail=(1,0,None)
>      app.name='Thunderbird' name='None' role='table cell' state='enabled 
> focusable focused opaque selectable selected sensitive showing vertical 
> visible' relations='node child of'
> Finding top-level object for source.name=
> --> obj.name=
> --> obj.name=
> --> obj.name=
> --> obj.name=Inbox - informal - Mozilla Thunderbird
> Finding top-level object for source.name=
> --> obj.name=
> --> obj.name=
> --> obj.name=
> --> obj.name=Inbox - informal - Mozilla Thunderbird
> LOCUS OF FOCUS: app='Thunderbird' name='[Bug 618589] when debugging in 
> eclipse, sometimes orca reads the same line twice' role='table cell'
>                  event='object:state-changed:focused'
> 
> Traceback (most recent call last):
>    File 
> "/data/software/orca/dev/lib/python2.6/site-packages/orca/focus_tracking_presenter.py", 
> line 709, in _processObjectEvent
>      s.processObjectEvent(event)
>    File 
> "/data/software/orca/dev/lib/python2.6/site-packages/orca/script.py", 
> line 383, in processObjectEvent
>      self.listeners[key](event)
>    File 
> "/data/software/orca/dev/lib/python2.6/site-packages/orca/scripts/apps/Thunderbird/script.py", 
> line 456, in onStateFocused
>      Gecko.Script.onStateChanged(self, event)
>    File 
> "/data/software/orca/dev/lib/python2.6/site-packages/orca/scripts/toolkits/Gecko/script.py", 
> line 1824, in onStateChanged
>      default.Script.onStateChanged(self, event)
>    File 
> "/data/software/orca/dev/lib/python2.6/site-packages/orca/default.py", 
> line 2982, in onStateChanged
>      self.onFocus(event)
>    File 
> "/data/software/orca/dev/lib/python2.6/site-packages/orca/scripts/apps/Thunderbird/script.py", 
> line 277, in onFocus
>      orca.setLocusOfFocus(event, acc, force=force)
>    File 
> "/data/software/orca/dev/lib/python2.6/site-packages/orca/orca.py", line 
> 263, in setLocusOfFocus
>      orca_state.locusOfFocus)
>    File 
> "/data/software/orca/dev/lib/python2.6/site-packages/orca/focus_tracking_presenter.py", 
> line 1035, in locusOfFocusChanged
>      newLocusOfFocus)
>    File 
> "/data/software/orca/dev/lib/python2.6/site-packages/orca/scripts/apps/Thunderbird/script.py", 
> line 398, in locusOfFocusChanged
>      string = orca_state.lastNonModifierKeyEvent.event_string
> AttributeError: 'NoneType' object has no attribute 'event_string'
> 
> ^^^^^ PROCESS OBJECT EVENT object:state-changed:focused ^^^^^