LaTeX parser fails on nested math environments when $$ is used

[cazgp]

This MWE compiles fine in latex.

\documentclass{article}

\begin{document}
$$
{\mbox{\boldmath $\theta $}}_2||^2
$$
\end{document}

However, pandoc fails when reading it:

$ pandoc -f latex problem.tex -o test.xml
pandoc: 
Error at "source" (line 5, column 33):
unexpected "^"
expecting "%", lf new-line, "\\", "{", "-", "``", "\8220", "\"`", "\"", "`", "\8216", "''", "\8221", "'", "\8217", "~", "$$", "$", "^^", "&" or \end{document}
{\mbox{\boldmath $\theta $}}_2||^2

If, however, the $$ delimiters are changed to \begin{displaymath}, then it works fine.

[jgm]

This issue should really be in jgm/texmath, which handles
math for pandoc.

texmath doesn't handle well commands that act as "switches",
like \boldmath. It likes commands with explicit arguments,
such as \mathbf. This could be improved in future versions.

Note that you should be able to do:

\mbox{$\mathbf{\theta}$}_2||^2

[cazgp]

Unfortunately I don't have much control over the document other than that which can be done programmatically.

How come it works fine with \begin{displaymath}?

[cazgp]

Closed in favour of jgm/texmath#93

[jgm]

OK, I looked into this further and found I couldn't reproduce the problem. You are undoubtedly using an older version of pandoc -- it would have helped to have had the pandoc version in the bug report.
(See CONTRIBUTING.md)

I do not get an error with pandoc problem.tex -o test.xml.
Moreover I get exactly the same output if I use \begin{displaymath}...\end{displaymath}.

Note that in neither case do I get mathml; that's because texmath doesn't handle \boldmath as noted above. I still don't get mathml when I use \textbf as suggested. This is because texmath can only handle simple \mbox environments which embed regular text.