Problem with tax on invoice line item. m2m problem?

[michafn]

I am trying to add an invoice position with tax. This does not work no matter how i try. I am passing an array of line_items such as:

{ 'account_id': 162, 'name': "product a", 'quantity': 1, 'price_unit': 17,'invoice_line_tax_ids':[6, 0, [12]],'product_id':1}

this should add the tax with id=12 to the line item. However this does not work. No tax is added. Any hints? Could this be a problem of m2m? invoice_line_tax_ids is a m2m field.