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)

addons/account/models/account_move.py
partial_rec_set[x] = None
            digits_rounding_precision = aml_set[0].company_id.currency_id.rounding
            if float_compare(total_debit, total_credit, precision_rounding=digits_rounding_precision) == 0 \
              or (currency and float_is_zero(total_amount_currency, precision_rounding=currency.rounding)):
                
                exchange_rate_entries = self.env['account.move'].search([('rate_diff_partial_rec_id', 'in', [x.id for x in partial_rec_set.keys()])])
        
        reversed_moves = exchange_rate_entries.reverse_moves()
        
        pairs_to_rec = []
        for rev_move in self.env['account.move'].browse(reversed_moves):
            if not rev_move.rate_diff_partial_rec_id:
                continue
            origin_move = exchange_rate_entries.filtered(lambda x: x.rate_diff_partial_rec_id == rev_move.rate_diff_partial_rec_id)
            for acm_line in rev_move.line_ids:
                if acm_line.account_id.reconcile:
                    for origin_line in origin_move.line_ids:
                        if origin_line.account_id == acm_line.account_id and origin_line.debit == acm_line.credit and origin_line.credit == acm_line.debit:
                            to_unlink |= origin_line.matched_debit_ids | origin_line.matched_credit_ids
                            to_rec = origin_line + acm_line
                            pairs_to_rec.append(to_rec)
        
        exchange_rate_entries.write({'rate_diff_partial_rec_id': False})
        
        res = super(AccountPartialReconcile, to_unlink).unlink()
        
        for to_rec in pairs_to_rec:
            to_rec.reconcile()
        return res