Use the context for the ModelList when instantiate record to be appended

Since changeset 9ed64cecb732, we ensure that the context of the instance is
the same as the context of the ModelList.

issue7384
review50301002

proteus/__init__.py

@@ -954,7 +954,7 @@ class Model(object):
                         definition, [], self, field)
                     config = Relation._config
                     with config.reset_context(), \
-                            config.set_context(self._context):
+                            config.set_context(records._get_context()):
                         for vals in (value or []):
                             record = Relation()
                             record._default_set(vals)
@@ -1053,9 +1053,11 @@ class Model(object):
                 Relation = Model.get(
                     self._fields[field]['relation'], self._config)
                 config = Relation._config
-                with config.reset_context(), config.set_context(self._context):
+                records = getattr(self, field)
+                with config.reset_context(), \
+                        config.set_context(records._get_context()):
                     record = Relation(_default=False, **vals)
-                getattr(self, field).append(record)
+                records.append(record)
         else:
             self._values[field] = value
         self._changed.add(field)