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).


odoo/fields.py
""" Return a domain representing a condition on ``self``. """
        if isinstance(self.search, basestring):
            return getattr(records, self.search)(operator, value)
        else:
            return self.search(records, operator, value)
    
    #
    
    #
    def modified(self, records):
        """ Notify that field ``self`` has been modified on ``records``: prepare the
            fields/records to recompute, and return a spec indicating what to
            invalidate.
        """
        
        spec = [(self, records._ids)]
        
        bymodel = defaultdict(lambda: defaultdict(list))
        for field, path in records._field_triggers[self]:
            bymodel[field.model_name][path].append(field)
        for model_name, bypath in bymodel.iteritems():
            for path, fields in bypath.iteritems():
                if path and any(field.compute and field.store for field in fields):
                    
                    stored = set(field for field in fields if field.compute and field.store)
                    fields = set(fields) - stored
                    if path == 'id':
                        target0 = records