1. `copy_cache` in `models.py` recursively copies the caches to environment, 
2. which in
```python
def _compute_related(self, records):
        """ Compute the related field ``self`` on ``records``. """
        others = records.sudo() if self.related_sudo else records
        if records.env != others.env:
            copy_cache(records - records.filtered('id'), others.env)
        values = list(others)
        for name in self.related[:-1]:
            values = [first(value[name]) for value in values]
        for record, value in zip(records, values):
            record[self.name] = value[self.related_field.name]
```
3. copies failing cache values that have been produce previously by this line:

`models.py : def _prefetch_field()`
```python

        try:
            # THIS ONE
            result = records.read([f.name for f in fs], load='_classic_write')
        except AccessError:
            # not all records may be accessible, try with only current record
            result = self.read([f.name for f in fs], load='_classic_write')
```
I checked it's exactly the same `FailedValue` object, which is later accessed without intent (not refreshed) by the fact that the buggy environment is copied to sudo (and not refreshed).


""" Convert a :class:`datetime` value into the format expected by the ORM. """
        return value.strftime(DATETIME_FORMAT) if value else False
    def convert_to_cache(self, value, record, validate=True):
        if not value:
            return False
        if isinstance(value, basestring):
            if validate:
                
                self.from_string(value)
            value = value[:DATETIME_LENGTH]
            if len(value) == DATE_LENGTH:
                value += " 00:00:00"
            return value
        return self.to_string(value)
    def convert_to_export(self, value, record):
        if not value:
            return ''
        return self.from_string(value) if record._context.get('export_raw_data') else ustr(value)
    def convert_to_display_name(self, value, record):
        assert record, 'Record expected'
        return Datetime.to_string(Datetime.context_timestamp(record, Datetime.from_string(value)))
class Binary(Field):