diff --git a/odoo/addons/test_new_api/tests/test_new_fields.py b/odoo/addons/test_new_api/tests/test_new_fields.py
index 10edaa907f4..492255df83e 100644
--- a/odoo/addons/test_new_api/tests/test_new_fields.py
+++ b/odoo/addons/test_new_api/tests/test_new_fields.py
@@ -958,9 +958,9 @@ class TestFields(common.TransactionCase):
         # no value gives the default value
         new_disc = discussion.new({'name': "Foo"})
         self.assertEqual(new_disc.categories._origin, cat1)
-        # value is combined with default value
+        # value overrides default value
         new_disc = discussion.new({'name': "Foo", 'categories': [(4, cat2.id)]})
-        self.assertEqual(new_disc.categories._origin, cat1 + cat2)
+        self.assertEqual(new_disc.categories._origin, cat2)
 
     def test_40_new_fields(self):
         """ Test new records with relational fields. """
diff --git a/odoo/fields.py b/odoo/fields.py
index 87718a00da0..033aa713ae6 100644
--- a/odoo/fields.py
+++ b/odoo/fields.py
@@ -2321,7 +2321,7 @@ class _RelationalMulti(_Relational):
             else:
                 browse = comodel.browse
             # determine the value ids
-            ids = OrderedSet(record[self.name]._ids)
+            ids = OrderedSet(record[self.name]._ids if validate else ())
             # modify ids with the commands
             for command in value:
                 if isinstance(command, (tuple, list)):