with tagging loaded optional arg of amsthm cannot contain brackets

[mbertucci47]

The usual thing to do is place the argument in braces but that doesn't work with the tagging code.

\DocumentMetadata
  {
    lang=en-US,
    pdfversion=2.0,
    pdfstandard=ua-2,
    testphase={phase-III,math,title,table,firstaid}
  }
\documentclass{article}

\usepackage{amsthm}

\newtheorem{theorem}{Theorem}

\begin{document}

\begin{theorem}[{\cite[abc]{dihe:newdir}}]
text
\end{theorem}

\begin{thebibliography}{9}
\bibitem{dihe:newdir}
W.~Diffie and E.~Hellman, \emph{New directions in cryptography}, IEEE
Transactions on Information Theory \textbf{22} (1976), no.~5, 644--654.
\end{thebibliography}

\end{document}

errors with

! Argument of \@citex@checkblank has an extra }.

It works with two pairs of braces though.

\begin{theorem}[{{\cite[abc]{dihe:newdir}}}]

So I'm guessing somewhere in the code a pair of braces should be added.