statusbar widget does not trigger on_change function

OpenERP 7.0 nightly build: 20130417-232500

Description:
If you have a clickable statusbar widget, changing the stage does not trigger the on_change function.
I have found this problem trying to use the new unified state/stage feature introduced with OE7.0 myself, but you can see how it is already happening in the CRM module. Leads have a clickable statusbar with an on_change function defined in crm/crm_lead_view.xml:102 but that function is only called manually from the python code in the server side when the user clicks the "Cancel case" button (which calls case_cancel->case_set->stage_set->onchange_function).

Steps to reproduce:
1- Create an empty database
2- Install CRM app
3- Run the server in a debugging environment and set a breakpoint inside the onchange_stage_id function (crm/crm_lead.py:332)
4- Create a lead (you will reach the breakpoint when creating it, that's fine, just continue)
5- Click on any stage on the statusbar. You will see how the on_change function isn't called.
6- Save the lead if you hadn't yet and click on the "Cancel case" button. You will see how the function is called server side (check stack)

Whenever you click on the satusbar, the record is beign saved with a different stage_id, so it is changing and the on_change function should have been called.