Added release note and regression test for refs #21643.

This will be backported to stable/1.6.x along with the original fix.

tests/expressions_regress/tests.py

@@ -281,6 +281,13 @@ class FTimeDeltaTests(TestCase):
         q2 = str(queryset.query)
         self.assertEqual(q1, q2)
 
+    def test_query_clone(self):
+        # Ticket #21643
+        qs = Experiment.objects.filter(end__lt=F('start') + datetime.timedelta(hours=1))
+        qs2 = qs.all()
+        list(qs)
+        list(qs2)
+
     def test_delta_add(self):
         for i in range(len(self.deltas)):
             delta = self.deltas[i]