In my case it was another module that introduced a bug :

def action_invoice_create(self, grouped=False, final=False):
    # Wrong line
    # res = super(SaleOrder, self).action_invoice_create()
	​ # Correct line
	​ res = super(SaleOrder, self).action_invoice_create(grouped, final)    
    for inv in res :
        invoice = self.env['account.invoice'].browse(inv)
        invoice._onchange_payment_term_date_invoice()
        invoice._get_affaccturage()

    return res

You have to pass final = True for this to work!!

@api.multi
def action_invoice_create(self, grouped=False, final=False):
invoice_id = super(SaleOrder, self).action_invoice_create(grouped, final)
return invoice_id

Hi, @Kent, 

Have the same problem and still haven't found the spected behaviour neither from a SO nor an invoice. 

Did you find the solution?

Thanks a lot, 

Pere