Bug confirmed, thank you very much.
VALUES is not involved, the bug is also triggered via (for (a b) = (list 2 1))
(deftest values.previous (equal (iter '((2 1 nil nil) (2 1 2 1) (2 1 2 1))) T)
Why didn't you write (deftest value.previous (iter #) ((2 1 nil nil) ...)) ? RT/DEFTEST output would then be more informative.
Regards, Jorg Hohle.