[web2py] session.flash is None when manually logging out

[danny]

Hello. I'm trying to customize the login and register forms as follows:

   - user() function does not return auth(), instead display two forms 
   separately like this:

      {{if not auth.is_logged_in():}}
      {{login_form = auth.login()}}
      {{=login_form.custom.begin}}
      ...
      {{=login_form.custom.submit}}
      {{=login_form.custom.end}}

      {{reg_form = auth.register()}}
      {{=reg_form.custom.begin}}
      ...
      {{=reg_form.custom.submit}}
      {{=reg_form.custom.end}}
      {{pass}}

   - Inside user() function it logs the user out manually when "http://.../[
   app]/default/user/logout" is requested:
   
    if request.args(0) == 'logout':
        session.flash = T('You are logged out.')
        auth.logout()

Everything works except session.flash is wiped clean when auth.logout() 
automatically redirects to default/index. How can I keep session.flash 
after redirect? Thanks.