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
date = date or fields.Date.today()
        reversed_moves = self.env['account.move']
        for ac_move in self:
            reversed_move = ac_move.copy(default={'date': date,
                'journal_id': journal_id.id if journal_id else ac_move.journal_id.id,
                'ref': _('reversal of: ') + ac_move.name})
            for acm_line in reversed_move.line_ids:
                acm_line.with_context(check_move_validity=False).write({
                    'debit': acm_line.credit,
                    'credit': acm_line.debit,
                    'amount_currency': -acm_line.amount_currency
                    })
            reversed_moves |= reversed_move
        if reversed_moves:
            reversed_moves._post_validate()
            reversed_moves.post()
            return [x.id for x in reversed_moves]
        return []
    @api.multi
    def open_reconcile_view(self):