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)

'debit': amount_diff < 0 and -amount_diff or 0.0,
                'credit': amount_diff > 0 and amount_diff or 0.0,
                'account_id': rec.debit_move_id.account_id.id,
                'move_id': move.id,
                'currency_id': currency.id,
                'amount_currency': -diff_in_currency,
                'partner_id': rec.debit_move_id.partner_id.id,
            })
            rec.env['account.move.line'].create({
                'name': _('Currency exchange rate difference'),
                'debit': amount_diff > 0 and amount_diff or 0.0,
                'credit': amount_diff < 0 and -amount_diff or 0.0,
                'account_id': amount_diff > 0 and rec.company_id.currency_exchange_journal_id.default_debit_account_id.id or rec.company_id.currency_exchange_journal_id.default_credit_account_id.id,
                'move_id': move.id,
                'currency_id': currency.id,
                'amount_currency': diff_in_currency,
                'partner_id': rec.debit_move_id.partner_id.id,
            })
            for aml in aml_to_fix:
                partial_rec = rec.env['account.partial.reconcile'].create({
                    'debit_move_id': aml.credit and line_to_reconcile.id or aml.id,
                    'credit_move_id': aml.debit and line_to_reconcile.id or aml.id,
                    'amount': abs(aml.amount_residual),
                    'amount_currency': abs(aml.amount_residual_currency),
                    'currency_id': currency.id,
                })
            move.post()
        return line_to_reconcile.id, partial_rec.id
    @api.model
    def create(self, vals):