[page reload] when active_id is used in context, (i.e. after a tree_but_open)

How to reproduce :

- open the account chart (hierarchical view)
- click on an account to open it
- reload the page

Client Traceback (most recent call last):
  File "/home/dadafkas/projets/anybox/anytracker/buildout/parts/openerp-6.1-20120831-231939/openerp/addons/web/common/http.py", line 180, in dispatch
    response["result"] = method(controller, self, **self.params)
  File "/home/dadafkas/projets/anybox/anytracker/buildout/parts/openerp-6.1-20120831-231939/openerp/addons/web/controllers/main.py", line 1553, in load
    value = clean_action(req, action[0], do_not_eval)
  File "/home/dadafkas/projets/anybox/anytracker/buildout/parts/openerp-6.1-20120831-231939/openerp/addons/web/controllers/main.py", line 692, in clean_action
    action['context'] = eval( action['context'], eval_ctx ) or {}
  File "<string>", line 1, in <module>
NameError: name 'active_id' is not defined

-----------------------------
Quick analysis :

The missing active_id is required by this view : account/account_view.xml:1298

            <field name="context">{'search_default_account_id': [active_id]}</field>

The problem is that the active_id is lost on the page reload.