buffer-face-set changes the fringe, is it a bug?

[Gregory Heytings]

Hi list,

Is the following behavior expected, or is it a bug?

(set-face-attribute 'fringe nil :background "red")
(let ((o (make-overlay 0 1)) (s "_"))
  (put-text-property 0 1 'display '(left-fringe question-mark) s)
  (overlay-put o 'after-string s))

This puts a question mark in the left fringe.  At least on Emacs 26.3 
(started with emacs -Q), after:

(buffer-face-set '(:background "yellow"))

the background of the buffer *and* the question mark in the fringe become 
yellow.  I would have expected that the background of the question mark 
would still be red.

Gregory