Pb with complex domain expressions

I have a problem with complex domain expressions ; it may be a bug of the OpenERP server, but it may also be a bad domain expression due to a bad comprehension of the way it is supposed to work.

In an ir.actions.act_window on the object account.invoice :

1) I want to filter on open invoice/refunds that are either from Asustek with country = Taiwan or from Direct PC with country = Belgium, so I write the following expression :

<field name="domain">['&amp;', '|', '&amp;', ('address_invoice_id.country_id.name', '=', 'Taiwan'), ('partner_id.name', '=', 'ASUStek'), '&amp;', ('address_invoice_id.country_id.name', '=', 'Belgium'), ('partner_id.name', '=', 'Distrib PC'), ('state', '=', 'open')]</field>

Result : it works OK.

2) I want to filter on open customer invoices that are either from Asustek with country = Taiwan or from Direct PC with country = Belgium, so I write the following expression :

<field name="domain">['&amp;', '&amp;', '|', '&amp;', ('address_invoice_id.country_id.name', '=', 'Taiwan'), ('partner_id.name', '=', 'ASUStek'), '&amp;', ('address_invoice_id.country_id.name', '=', 'Belgium'), ('partner_id.name', '=', 'Distrib PC'), ('state', '=', 'open'), ('type', '=', 'out_invoice')]</field>

Result : NOT OK, I get ALL the invoices !

I have this problem with OpenERP server branch 5.0 and branch 6.0 ; I wanted to test on trunk, but I can't find the "Modules" menu entry to install my module !

By the way, my source of information about complex domain expressions is this one :
http://christophe-simonis-at-tiny.blogspot.com/2008/08/new-new-domain-notation.html
plus wikipedia to understand "polish expressions" and "arity".