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
self._update_check()
        move_ids = set()
        for line in self:
            if line.move_id.id not in move_ids:
                move_ids.add(line.move_id.id)
        result = super(AccountMoveLine, self).unlink()
        if self._context.get('check_move_validity', True) and move_ids:
            self.env['account.move'].browse(list(move_ids))._post_validate()
        return result
    @api.multi
    def write(self, vals):
        if vals.get('tax_line_id') or vals.get('tax_ids'):
            raise UserError(_('You cannot change the tax, you should remove and recreate lines.'))
        if ('account_id' in vals) and self.env['account.account'].browse(vals['account_id']).deprecated:
            raise UserError(_('You cannot use deprecated account.'))
        if any(key in vals for key in ('account_id', 'journal_id', 'date', 'move_id', 'debit', 'credit')):
            self._update_check()
        if not self._context.get('allow_amount_currency') and any(key in vals for key in ('amount_currency', 'currency_id')):
            
            
            self._update_check()
        
        if vals.get('expected_pay_date') and self.invoice_id:
            msg = _('New expected payment date: ') + vals['expected_pay_date'] + '.\n' + vals.get('internal_note', '')
            self.invoice_id.message_post(body=msg) 
        
        if 'statement_id' in vals and self.payment_id: