My .emacs says:

(custom-set-faces '(mode-line ((nil (:background "yellow")))))
(custom-set-variables '(default-frame-alist '((font . "10x20"))))

but the mode line isn't yellow.

If I remove the 2nd line, the mode line is yellow.

Setting the font shouldn't stop me setting the mode-line face, should it?

This was working fine until a day or two ago, in CVS trunk.