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
for line in self:
            company_currency = line.account_id.company_id.currency_id
            ret_line = {
                'id': line.id,
                'name': line.name != '/' and line.move_id.name + ': ' + line.name or line.move_id.name,
                'ref': line.move_id.ref or '',
                
                
                'already_paid': line.account_id.internal_type == 'liquidity',
                'account_code': line.account_id.code,
                'account_name': line.account_id.name,
                'account_type': line.account_id.internal_type,
                'date_maturity': line.date_maturity,
                'date': line.date,
                'journal_name': line.journal_id.name,
                'partner_id': line.partner_id.id,
                'partner_name': line.partner_id.name,
                'currency_id': (line.currency_id and line.amount_currency) and line.currency_id.id or False,
            }
            debit = line.debit
            credit = line.credit
            amount = line.amount_residual
            amount_currency = line.amount_residual_currency
            
            if line.account_id.internal_type == 'liquidity':
                amount = abs(debit - credit)
                amount_currency = abs(line.amount_currency)
            
            target_currency = target_currency or company_currency
            line_currency = (line.currency_id and line.amount_currency) and line.currency_id or company_currency