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_currency_str = ""
            total_amount_currency_str = ""
            if line_currency != company_currency:
                total_amount = line.amount_currency
                actual_debit = debit > 0 and amount_currency or 0.0
                actual_credit = credit > 0 and -amount_currency or 0.0
            else:
                total_amount = abs(debit - credit)
                actual_debit = debit > 0 and amount or 0.0
                actual_credit = credit > 0 and -amount or 0.0
            if line_currency != target_currency:
                amount_currency_str = formatLang(self.env, abs(actual_debit or actual_credit), currency_obj=line_currency)
                total_amount_currency_str = formatLang(self.env, total_amount, currency_obj=line_currency)
                ctx = context.copy()
                ctx.update({'date': target_date or line.date})
                total_amount = line_currency.with_context(ctx).compute(total_amount, target_currency)
                actual_debit = line_currency.with_context(ctx).compute(actual_debit, target_currency)
                actual_credit = line_currency.with_context(ctx).compute(actual_credit, target_currency)
            amount_str = formatLang(self.env, abs(actual_debit or actual_credit), currency_obj=target_currency)
            total_amount_str = formatLang(self.env, total_amount, currency_obj=target_currency)
            ret_line['debit'] = abs(actual_debit)
            ret_line['credit'] = abs(actual_credit)
            ret_line['amount_str'] = amount_str
            ret_line['total_amount_str'] = total_amount_str
            ret_line['amount_currency_str'] = amount_currency_str
            ret_line['total_amount_currency_str'] = total_amount_currency_str
            ret.append(ret_line)
        return ret
    @api.v7
    def process_reconciliations(self, cr, uid, data, context=None):