Impacted versions: 9.0, 9.0 enterprise

Steps to reproduce:
On current runbot duplicate any posted journal entry which is balanced

Current behavior:
Error message "Cannot create unbalanced entry" is shown

Expected behavior:
New Journal entry is created in state 'draft'

Video/Screenshot link (optional):
![selection_268](https://cloud.githubusercontent.com/assets/14974044/15007437/41f45a56-11d9-11e6-84f3-b297befaa521.png)

for move_line in self:
            if move_line.journal_id.type in ('sale', 'purchase'):
                move_line.debit_cash_basis = move_line.debit * move_line.move_id.matched_percentage
                move_line.credit_cash_basis = move_line.credit * move_line.move_id.matched_percentage
            else:
                move_line.debit_cash_basis = move_line.debit
                move_line.credit_cash_basis = move_line.credit
            move_line.balance_cash_basis = move_line.debit_cash_basis - move_line.credit_cash_basis
    @api.one
    @api.depends('move_id.line_ids')
    def _get_counterpart(self):
        counterpart = set()
        for line in self.move_id.line_ids:
            if (line.account_id.code != self.account_id.code):
                counterpart.add(line.account_id.code)
        if len(counterpart) > 2:
            counterpart = counterpart[0:2] + ["..."]
        self.counterpart = ",".join(counterpart)
    name = fields.Char(required=True, string="Label")
    quantity = fields.Float(digits=(16, 2),
        help="The optional quantity expressed by this line, eg: number of product sold. The quantity is not a legal requirement but is very useful for some reports.")
    product_uom_id = fields.Many2one('product.uom', string='Unit of Measure')
    product_id = fields.Many2one('product.product', string='Product')