[AUCTeX] This code works in some TeX buffers and not in some others. Any ideas?

[Marcin Borkowski]

Hi all,

I don't want my tildes to stand out too much, so I have this in my
init.el:

(add-hook
 'TeX-mode-hook
 (lambda ()
   (font-lock-add-keywords
    nil
    '(("~" . 'font-latex-sedate-face)))))

In some LaTeX buffers it works, in some not.  Why this might be?  How to
even debug this?

(AUCTeX auctex-11.89.1, from Elpa)

Best,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University