bug#31722: 12.1.1; TeX Fold fontification problem

[Marco Falconi]

I have a custom definition of math macros to be folded. It is the following 
(taken from
.emacs in the customize part, I have set it using customize):

'(LaTeX-fold-math-spec-list
   (quote
    (("[{1}/{2}]"
      ("frac" "tfrac"))
     ("[{1}⇣{2}]"
      ("underset"))
     ("[{1}⇡{2}]"
      ("overset"))
     ("︷[{1}]"
      ("underbrace"))
     ("√[{1}]"
      ("sqrt")))))

In the ones with two arguments (frac, tfrac, underset, overset), the first 
argument gets
fontified in the folded string, but the second one is not fontified (in the 
unfolded
string, everything is fontified correctly). This macro for example has such 
behavior:

\underset{\hslash\to 0}{ \longrightarrow}

The macros with just one argument are fontified correctly also when folded.

Emacs  : GNU Emacs 26.1 (build 1, x86_64-apple-darwin13.4.0, Carbon Version 157 
AppKit 1265.21)
 of 2018-04-15
Package: 12.1.1

current state:
==============
(setq
 AUCTeX-date "2018-03-20"
 window-system 'mac
 LaTeX-version "2e"
 TeX-style-path '("/usr/local/var/auctex" 
"/Users/lobo/.emacs.d/elpa/auctex-12.1.1/style" 
"/Users/lobo/.emacs.d/auctex/auto"
                  "/Users/lobo/.emacs.d/auctex/style" "auto" "style")
 TeX-auto-save t
 TeX-parse-self t
 TeX-master nil
 TeX-command-list '(("TeX" "%(PDF)%(tex) %(file-line-error) %(extraopts) 
%`%S%(PDFout)%(mode)%' %t" TeX-run-TeX nil
                     (plain-tex-mode texinfo-mode ams-tex-mode) :help "Run 
plain TeX")
                    ("LaTeX" "%`%l%(mode)%' %t" TeX-run-TeX nil (latex-mode 
doctex-mode) :help "Run LaTeX")
                    ("Makeinfo" "makeinfo %(extraopts) %t" TeX-run-compile nil 
(texinfo-mode) :help "Run Makeinfo with Info output")
                    ("Makeinfo HTML" "makeinfo %(extraopts) --html %t" 
TeX-run-compile nil (texinfo-mode) :help "Run Makeinfo with HTML output")
                    ("AmSTeX" "amstex %(PDFout) %(extraopts) %`%S%(mode)%' %t" 
TeX-run-TeX nil (ams-tex-mode) :help "Run AMSTeX")
                    ("ConTeXt" "%(cntxcom) --once --texutil %(extraopts) 
%(execopts)%t" TeX-run-TeX nil (context-mode) :help "Run ConTeXt once")
                    ("ConTeXt Full" "%(cntxcom) %(extraopts) %(execopts)%t" 
TeX-run-TeX nil (context-mode) :help "Run ConTeXt until completion")
                    ("BibTeX" "bibtex %s" TeX-run-BibTeX nil t :help "Run 
BibTeX") ("Biber" "biber %s" TeX-run-Biber nil t :help "Run Biber")
                    ("View" "%V" TeX-run-discard-or-function t t :help "Run 
Viewer") ("Print" "%p" TeX-run-command t t :help "Print the file")
                    ("Queue" "%q" TeX-run-background nil t :help "View the 
printer queue" :visible TeX-queue-command)
                    ("File" "%(o?)dvips %d -o %f " TeX-run-dvips t t :help 
"Generate PostScript file")
                    ("Dvips" "%(o?)dvips %d -o %f " TeX-run-dvips nil t :help 
"Convert DVI file to PostScript")
                    ("Dvipdfmx" "dvipdfmx %d" TeX-run-dvipdfmx nil t :help 
"Convert DVI file to PDF with dvipdfmx")
                    ("Ps2pdf" "ps2pdf %f" TeX-run-ps2pdf nil t :help "Convert 
PostScript file to PDF")
                    ("Glossaries" "makeglossaries %s" TeX-run-command nil t 
:help "Run makeglossaries to create glossary file")
                    ("Index" "makeindex %s" TeX-run-index nil t :help "Run 
makeindex to create index file")
                    ("upMendex" "upmendex %s" TeX-run-index t t :help "Run 
upmendex to create index file")
                    ("Xindy" "texindy %s" TeX-run-command nil t :help "Run 
xindy to create index file")
                    ("Check" "lacheck %s" TeX-run-compile nil (latex-mode) 
:help "Check LaTeX file for correctness")
                    ("ChkTeX" "chktex -v6 %s" TeX-run-compile nil (latex-mode) 
:help "Check LaTeX file for common mistakes")
                    ("Spell" "(TeX-ispell-document \"\")" TeX-run-function nil 
t :help "Spell-check the document")
                    ("Clean" "TeX-clean" TeX-run-function nil t :help "Delete 
generated intermediate files")
                    ("Clean All" "(TeX-clean t)" TeX-run-function nil t :help 
"Delete generated intermediate and output files")
                    ("Other" "" TeX-run-command t t :help "Run an arbitrary 
command") ("Forward" "pdf-sync-forward-search" TeX-run-function nil t))
 )