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).


record._prefetch[res_model].add(res_id)
            return (res_model, res_id)
        if isinstance(value, BaseModel):
            if not validate or (value._name in self.get_values(record.env) and len(value) <= 1):
                return process(value._name, value.id) if value else False
        elif isinstance(value, basestring):
            res_model, res_id = value.split(',')
            if record.env[res_model].browse(int(res_id)).exists():
                return process(res_model, int(res_id))
            else:
                return False
        elif not value:
            return False
        raise ValueError("Wrong value for %s: %r" % (self, value))
    def convert_to_record(self, value, record):
        return value and record.env[value[0]].browse([value[1]], record._prefetch)
    def convert_to_read(self, value, record, use_name_get=True):
        return "%s,%s" % (value._name, value.id) if value else False
    def convert_to_export(self, value, record):
        return value.name_get()[0][1] if value else ''
    def convert_to_display_name(self, value, record):
        return ustr(value and value.display_name)
class _Relational(Field):
    """ Abstract class for relational fields. """
    relational = True
    _slots = {
        'domain': [],                   
        'context': {},                  
    }
    def _setup_regular_base(self, model):