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)

amount_reconcile = min(sm_debit_move[field], -sm_credit_move[field])
        
        if amount_reconcile == sm_debit_move[field]:
            self -= sm_debit_move
        if amount_reconcile == -sm_credit_move[field]:
            self -= sm_credit_move
        
        currency = False
        amount_reconcile_currency = 0
        if sm_debit_move.currency_id == sm_credit_move.currency_id and sm_debit_move.currency_id.id:
            currency = sm_credit_move.currency_id.id
            amount_reconcile_currency = min(sm_debit_move.amount_residual_currency, -sm_credit_move.amount_residual_currency)
        amount_reconcile = min(sm_debit_move.amount_residual, -sm_credit_move.amount_residual)
        if self._context.get('skip_full_reconcile_check') == 'amount_currency_excluded':
            amount_reconcile_currency = 0.0
            currency = self._context.get('manual_full_reconcile_currency')
        elif self._context.get('skip_full_reconcile_check') == 'amount_currency_only':
            currency = self._context.get('manual_full_reconcile_currency')
        self.env['account.partial.reconcile'].create({
            'debit_move_id': sm_debit_move.id,
            'credit_move_id': sm_credit_move.id,
            'amount': amount_reconcile,
            'amount_currency': amount_reconcile_currency,
            'currency_id': currency,
        })
        
        return self.auto_reconcile_lines()
    @api.multi
    def reconcile(self, writeoff_acc_id=False, writeoff_journal_id=False):