Comment 4 for bug 1108801

in account/account_invoice.py
line 1679 insert
                val['id'] = tax['id']
line 1701 change to
                key = (val['tax_code_id'], val['base_code_id'], val['account_id'], val['account_analytic_id'], val['id'])

so it groups by tax ID, not just the tax code IDs