Pricelists are used only in sale, purchase, pos forms, not in invoice form, for that, the field should be add to the invoice form, to override methods product_id_change depending pricelist (eventually onchange_partner_id to get automatically the good pricelist) .

Difference between product price inherited from sale, purchase, pos in an invoice (without do a product onchange after creation of this invoice), and created an invoice directly without inherithing sale, purchase, pos, is due to onchange on field product_id.

Example :

for sale, pricelist is used to calculate price :

def product_id_change(self, cr, uid, ids, pricelist, product, qty=0,

uom=False, qty_uos=0, uos=False, name='', partner_id=False,

lang=False, update_tax=True, date_order=False, packaging=False, fiscal_position=False, flag=False, context=None):

.....................

price = self.pool.get('product.pricelist').price_get(cr, uid, [pricelist],

product, qty or 1.0, partner_id, {

'uom': uom or result.get('product_uom'),

'date': date_order,

})[pricelist]

...............................

for invoice, no pricelist used :

def product_id_change(self, product, uom_id, qty=0, name='', type='out_invoice',

partner_id=False, fposition_id=False, price_unit=False, currency_id=False,

company_id=None):

..................

if type in ('in_invoice', 'in_refund'):

values['price_unit'] = price_unit or product.standard_price

else:

values['price_unit'] = product.list_price

..................

It is enough clear ?

bye