symptom:
(custom-face-attributes-get 'font-lock-keyword-face nil)
==> (:foreground "Cyan1")
(set-face-attribute 'font-lock-keyword-face nil
:family "verdana")
(custom-face-attributes-get 'font-lock-keyword-face nil)
==> (:foreground "Cyan1" :family "verdana")
--------------------------------------------------------------
(set-face-attribute 'font-lock-keyword-face nil
:family 'unspecified)
(custom-face-attributes-get 'font-lock-keyword-face nil)
==> (:foreground "Cyan1" :family "verdana") ;; wasn't removed
--------------------------------------------------------------
my solution:
modify faces.el file
===============================================================
738c738
< (when (stringp family)
---
> (when (or (stringp family)(eq family 'unspecified))
741c741
< (when (stringp foundry)
---
> (when (or (stringp foundry)(eq foundry 'unspecified))
===============================================================