Mistake in LaTeX syntax not detected, strange pdf generated

[Alain.Cochard@unistra.fr]

I have file debug3.org which contains only 

   * strange
   #+begin_export latex 
   \[
     \text{a_b}
   \]
   #+end_export

Upon latex export (C-c C-e l o) the generated pdf shows a sequence of
4 "a subscript b" in a row (with 3 font sizes).

Result observed with various Org versions including

Org mode version 9.4.4 (release_9.4.4 @
/usr/share/emacs/27.2/lisp/org/)

with 'emacs -Q'.

NB: If I run pdflatex on the .tex created:

   pdflatex debug3.tex

I get

   ! Missing $ inserted.
   <inserted text> 
                   $
   l.31   \text{a_b}

and no pdf is generated.

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