Comment 1 for bug 1023721

A seemingly related issue on 1.0.57.66-5783625:

(defun find-foo (seq)
  (map nil
       (lambda (x)
         (declare (optimize speed))
         (when (eq x :foo)
           (return-from find-foo t)))
       seq))

; note: Allocating a value-cell at runtime for checking possibly out of extent exit via
; (RETURN-FROM FIND-FOO T). Use GO/RETURN-FROM with SAFETY 0, or declare the exit
; function DYNAMIC-EXTENT to avoid.

MAPCAR gives no note, but APPLY #'MAPCAR does.