The italic face no longer has slant: italic as specified in faces.el,  
but it has "underline" set instead.  This can be verified with M-x  
customize-face RET italic RET.

Last known "good" revision was 2c0a1f1 (Mon Jun 8, 15:04).
My current revision is 2583fe5 (Jun 11 02:34).

I believe this may have come with teh recent changes to the font  
selection mechanism by Adrian.   I've tested on NS only.