bzr explore fails to open branch with out-of-date working tree

I see this traceback in the console and nothing happens (of course) in the GUI.

Traceback (most recent call last):
  File "C:\work\Bazaar\plugins\explorer\lib\explorer.py", line 458, in do_open
    self.open_location(str(location))
  File "C:\work\Bazaar\plugins\explorer\lib\explorer.py", line 443, in open_loca
tion
    self.location_views.add_location(model)
  File "C:\work\Bazaar\plugins\explorer\lib\location.py", line 288, in add_locat
ion
    view = model.view()
  File "C:\work\Bazaar\plugins\explorer\lib\location.py", line 254, in view
    return view.ui()
  File "C:\work\Bazaar\plugins\explorer\lib\view_workingtree.py", line 67, in ui

    self.refresh_view()
  File "C:\work\Bazaar\plugins\explorer\lib\view_workingtree.py", line 71, in re
fresh_view
    self._collect_data()
  File "C:\work\Bazaar\plugins\explorer\lib\view_workingtree.py", line 86, in _c
ollect_data
    specific_files=specific_files, versioned=False)
  File "C:\work\Bazaar\plugins\explorer\lib\view_workingtree.py", line 291, in _
get_status_info
    raise errors.OutOfDateTree(wt)
bzrlib.errors.OutOfDateTree: Working tree is out of date, please run 'bzr update
'.