Inconsistent behavior with set-face-parent

If you evaluate the form (progn (defface foo '((t (:size "24pt"))) "foo face") (set-face-parent 'foo 'default) (customize-face 'foo)) in XEmacs 21.4.18 you'll get a customization buffer where the face sample is displayed in the size of the default face but the size specifier displays "24pt". If you invoke "State --> Set for Current Session" the face sample will be updated and be displayed with the 24pt size. Reading the doc string of `set-face-parent' I would not expect the face to keep its explicitely set size but I also would not expect to see the old size in the customization buffer. -- Ralf