Configuration:
- Company Currency: MXN
- Tax 16%.
- Multicurrency, MXN and USD.
- Decimal precision: 4
- Currency Data:
MXN: rate 1.0
USD rates

| Database time | rate | Local time (Mexico) | 
| --- | --- | --- |
| 2016-09-09 00:00:01 | 0.054440 | 2016-09-08 17:00:01 |
| 2016-10-11 00:00:01 | 0.051815 | 2016-10-10 17:00:01 |

Steps to reproduce:

1. Create an invoice for 600 USD  + tax (16%) with date 09/09/16 (September 9, 2016) and when you validate in the journal entry is $12,784.7172 MXN.
3. Create a bank statement in MXN and add a line with date 11/10/16 (October 11, 2016) and amount $13,372.80 MXN.
4. When reconcile select the invoice and there is a difference ($588.0828 MXN) add a line with the difference and select an account for the difference. 
<img width="607" alt="captura de pantalla 2016-11-04 a la s 17 23 26" src="https://cloud.githubusercontent.com/assets/6758279/20025385/749605a2-a2b3-11e6-8b1a-4e9fbf1521ed.png">

**Note that the amount of difference is $588.08 in when you select the account**

5. Click on reconcile.

Expected behavior:
- Reconcile the invoice and create account move.

Current behavior:
- Raise an error  `Wrong credit or debit value in accounting entry !`

![captura de pantalla 2016-11-01 a la s 19 18 52](https://cloud.githubusercontent.com/assets/6758279/19913537/1c272866-a069-11e6-9b06-5851681c7fa5.png)

addons/account/models/account_move.py
for move in self:
            if not move.journal_id.update_posted:
                raise UserError(_('You cannot modify a posted entry of this journal.\nFirst you should set the journal to allow cancelling entries.'))
        if self.ids:
            self._check_lock_date()
            self._cr.execute('UPDATE account_move '\
                       'SET state=%s '\
                       'WHERE id IN %s', ('draft', tuple(self.ids),))
            self.invalidate_cache()
        return True
    @api.multi
    def unlink(self):
        for move in self:
            
            move.line_ids._update_check()
            move.line_ids.unlink()
        return super(AccountMove, self).unlink()
    @api.multi
    def _post_validate(self):
        for move in self:
            if move.line_ids:
                if not all([x.company_id.id == move.company_id.id for x in move.line_ids]):
                    raise UserError(_("Cannot create moves for different companies."))
        self.assert_balanced()
        return self._check_lock_date()
    @api.multi
    def _check_lock_date(self):