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).


if self.type != field.type:
            raise TypeError("Type of related field %s is inconsistent with %s" % (self, field))
        
        self.depends = ('.'.join(self.related),)
        self.compute = self._compute_related
        if not (self.readonly or field.readonly):
            self.inverse = self._inverse_related
        if field._description_searchable:
            
            self.search = self._search_related
        
        for attr, prop in self.related_attrs:
            if not getattr(self, attr):
                setattr(self, attr, getattr(field, prop))
        for attr, value in field._attrs.iteritems():
            if attr not in self._attrs:
                setattr(self, attr, value)
        
        if not self.states and self.inherited:
            self.states = field.states
        
        if self.inherited and field.required:
            self.required = True
    def traverse_related(self, record):
        """ Traverse the fields of the related field `self` except for the last
        one, and return it as a pair `(last_record, last_field)`. """
        for name in self.related[:-1]:
            record = record[name][:1].with_prefetch(record._prefetch)
        return record, self.related_field
    def _compute_related(self, records):