Generating tmp.tex from [$$] block adds blank lines, breaking some environments

[dae]

A card with the following text:
[$$]
\begin{tikzcd}
PB \ar[r, "g^{-1}"] \ar[d, "k_"']
& PD \ar[d, "h_"] \
PC \ar[r, "f^{-1}"']
& PA
\end{tikzcd}
[/$$]

generates the following tmp.tex file:
[... preamble, including the needed \usepackage etc commands, snipped ...]
\begin{displaymath}
\begin{tikzcd}
PB \ar[r, "g^{-1}"] \ar[d, "k_*"']

& PD \ar[d, "h_*"] \

PC \ar[r, "f^{-1}"']

& PA
\end{tikzcd}

\end{displaymath}
\end{document}

which fails to compile, because of the blank lines. I don’t know why Anki is introducing these blank lines, and I don’t know how to stop it doing so.
Anki version:
Anki 24.06.3 (d678e39)
Python 3.9.18 Qt 6.6.2 PyQt 6.6.1
Platform: macOS-14.7-arm64-arm-64bit

Originally reported on https://forums.ankiweb.net/t/generating-tmp-tex-from-block-adds-blank-lines-breaking-some-environments/50169/2

[juliangilbey]

(And that forum post also has an analysis of the cause of the problem and a suggested resolution.)