account_id is mandatory, and is set thanks to an onchange of partner_id. But partner_id is not required, therefore, if you do not set a customer/supplier, there is no
account_id set by default.
On the purchase, the account_id was always invisible. Therefore, it was impossible to set the account_id if you did not set any supplier
On the sale, the account_id was invisible if you set the pay_now to pay later. Therefore, it was impossible to set an account_id if you did not set any customer and set pay later.
Anyway, now, account_id is always displayed, so the user can change the value of account_id if the default value provided is not was he wants, whatever the value of the other fields
bzr revid: dle@openerp.com-20140212142737-ox2l9twg3x6ywvqg
4ca9ae11a5