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).


'deprecated': None,             
        'related_field': None,          
        'group_operator': None,         
        'group_expand': None,           
        'prefetch': True,               
    }
    def __init__(self, string=Default, **kwargs):
        kwargs['string'] = string
        args = {key: val for key, val in kwargs.iteritems() if val is not Default}
        self.args = args or EMPTY_DICT
        self._setup_done = None
    def new(self, **kwargs):
        """ Return a field of the same type as ``self``, with its own parameters. """
        return type(self)(**kwargs)
    def __getattr__(self, name):
        """ Access non-slot field attribute. """
        try:
            return self._attrs[name]
        except KeyError:
            raise AttributeError(name)
    def __setattr__(self, name, value):
        """ Set slot or non-slot field attribute. """
        try:
            object.__setattr__(self, name, value)
        except AttributeError:
            if self._attrs:
                self._attrs[name] = value
            else:
                self._attrs = {name: value}     
    def set_all_attrs(self, attrs):