Patching apropos.el in the following manner seems to have fixed the problem.

(defun apropos-value-internal (predicate symbol function)
      (if (funcall predicate symbol)
          (progn
            (setq symbol (or (ignore-errors
                               (prin1-to-string (funcall function symbol)))
                             ""))
            (if (string-match apropos-regexp symbol)
                (progn
                  (if apropos-match-face
                      (put-text-property (match-beginning 0) (match-end 0)
                                         'face apropos-match-face
                                         symbol))
                  symbol)))))

Evgeni