wx dialog in tutorial examples is not able to be closed

Using the Canopy distribution (1.1.0-osx-64 on OSX 10.7.5), the example (http://docs.enthought.com/chaco/user_manual/tutorial_1.html#application-oriented-plotting) works in the Canopy Editor, but almost works correctly from the command line. This time, the expected plot appears, but it's not possible to close the window because of this error when clicking the 'window close' button:

Traceback (most recent call last):

  File "/Users/david/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/traitsui/wx/ui_live.py", line 333, in _on_close_page

    self._on_ok( event )

  File "/Users/david/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/traitsui/wx/ui_live.py", line 360, in _on_ok

    self.close( wx.ID_OK )

  File "/Users/david/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/traitsui/wx/ui_live.py", line 320, in close

    ui.finish()

  File "/Users/david/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/traitsui/ui.py", line 264, in finish

    self.reset( destroy = True )

  File "/Users/david/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/traitsui/ui.py", line 304, in reset

    editor.dispose()

  File "/Users/david/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/enable/component_editor.py", line 52, in dispose

    self._window.cleanup()

AttributeError: 'NoneType' object has no attribute 'cleanup'

By default my system seems to be using wx. If I do the following before running the command-line scripts:

$ export ETS_TOOLKIT=qt4

then the tutorial 'applications' do terminate correctly when run from the command line.