[Bug-AUCTeX] Auctex do not ask for the master file

[Olive]

I am using auctex 11.84 with emacs 21.4.2 (on GNU/Linux). I have put

(load "auctex.el" nil t t)
(setq TeX-auto-save t)
(setq TeX-parse-self t)
(setq TeX-master nil)

I have the problem that auctex never ask for the master file (even for 
files that does not contains \documentclass) and apparently always 
assume that the current file is the master file. Normally with 
TeX-master set to nil, it should ask. Notice that all works properly if 
I manually do a M-x TeX-master-file-ask

I am not sure it is a bug or if I have missed some things.

Olive