Setting a duplicate permission fails with error

[anonymous]

Traceback (most recent call last):
  File "C:\Program Files\ActiveState\Python\Lib\site-packages\trac\web\main.py", line 387, in dispatch_request
    dispatcher.dispatch(req)
  File "C:\Program Files\ActiveState\Python\Lib\site-packages\trac\web\main.py", line 237, in dispatch
    resp = chosen_handler.process_request(req)
  File "c:\program files\activestate\python\lib\site-packages\TracWebAdmin-0.1.2dev_r4240-py2.4.egg\webadmin\web_ui.py", line 109, in process_request
    path_info)
  File "c:\program files\activestate\python\lib\site-packages\TracWebAdmin-0.1.2dev_r4240-py2.4.egg\webadmin\perm.py", line 45, in process_admin_request
    perm.grant_permission(subject, action)
  File "C:\Program Files\ActiveState\Python\Lib\site-packages\trac\perm.py", line 190, in grant_permission
    self.store.grant_permission(username, action)
  File "C:\Program Files\ActiveState\Python\Lib\site-packages\trac\perm.py", line 143, in grant_permission
    (username, action))
  File "C:\Program Files\ActiveState\Python\Lib\site-packages\trac\db\util.py", line 50, in execute
    return self.cursor.execute(sql_escape_percent(sql), args)
  File "C:\Program Files\ActiveState\Python\Lib\site-packages\trac\db\sqlite_backend.py", line 56, in execute
    args or [])
  File "C:\Program Files\ActiveState\Python\Lib\site-packages\trac\db\sqlite_backend.py", line 48, in _rollback_on_error
    return function(self, *args, **kwargs)
IntegrityError: columns username, action are not unique