Gnome getting confused with mime types

[Olivier Ramare <ramare@math.univ-lille1.fr>]

Dear all,

  Sorry if my question does not belong to this
group --- Anyway, here is the file "HRIW2.tex":
----------------------------------------------
%\chapter{Brun sieve after Rankin's trick}
\label{Brun sieve after Rankin's trick}

We follow here \cite{Murty-Saradha*87}. \cite{Brun*19b}.

%%% Local Variables:
%%% mode: latex
%%% TeX-master: "HRIWLectures"
%%% End:
----------------------------------------------
This is a chapter of a book, chapter which I want to
open with emacs. However gnome always tells me
[translation approximate]:
-------------------------------------------------
Impossible to open HRIW2.tex
The name of this file "HRIW2.tex" indicates that it is
a "document TeX" file. The content of this file indicates
that it is a "script/MATLAB" file. [...]
-------------------------------------------------
Both Matlab script and tex files are to be opened
with emacs anyway (I do not use any matlab script!).
I tried to declare these files "certified" with
the proper icon attached to them, to no avail.

Since I'm writing a book, I will have quite a lot
of editing to do ...

What I would want:
-- a definite way to tell my system that I know
   the file I'm editing, once and for all.
-- but short of that, a way to trick the system
   into believing it is a tex file would be good.
   Or a way to trick it into not believing it is
   a matlab script. I tried to scan through
   /usr/share/gnome/mime[-info]? but found nothing
   relevant. And the file /usr/share/mime/magic
   is compiled. Can't even find where the mime
   type script/matlab is declared/defined

Any idea?
Many thanks in advance! [that's gnome2 -- and lenny]
Best,
Amities,
        Olivier