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).


""" Setup the attributes of a non-related field. """
        def make_depends(deps):
            return tuple(deps(model) if callable(deps) else deps)
        if isinstance(self.compute, basestring):
            
            self.depends = ()
            for method in resolve_mro(model, self.compute, callable):
                self.depends += make_depends(getattr(method, '_depends', ()))
        else:
            self.depends = make_depends(getattr(self.compute, '_depends', ()))
    def _setup_regular_full(self, model):
        """ Setup the inverse field(s) of ``self``. """
        pass
    #
    
    #
    def _setup_related_full(self, model):
        """ Setup the attributes of a related field. """
        
        if isinstance(self.related, basestring):
            self.related = tuple(self.related.split('.'))
        
        target = model
        for name in self.related:
            field = target._fields[name]
            field.setup_full(target)
            target = target[name]
        self.related_field = field