(defun test-check-syntax-table (begin end)
  (unless (eq (syntax-table) test-syntax-prop-mode-syntax-table)
    (error "syntax table is changed to %s during syntax propertize"
           (if (eq (syntax-table) (standard-syntax-table))
               'standard-syntax-table
             'other-syntax-table))))

(define-derived-mode test-syntax-prop-mode prog-mode "TestSyntaxProp"
  "A mode for testing syntax-propertize bug(?)."
  (setq-local syntax-propertize-function #'test-check-syntax-table)
  (setq-local font-lock-defaults
              '(nil nil nil nil nil
                (font-lock-syntactic-face-function . ignore)
                (parse-sexp-lookup-properties . t))))

(switch-to-buffer "tt")
(test-syntax-prop-mode)
(erase-buffer)
(insert "foo")
(with-syntax-table (standard-syntax-table)
  (scan-sexps 1 1))