Differentiated TOC/body section names in reledpar

In a reledpar project I'd like for some sections to appear in the TOC with different names than how they appear in the body. Normally this is straightforward: \section[name in TOC]{name in body}. However, this generates an error if attempted within reledpar (Argument of \ttl@straight@i has an extra }) or reledmac (Incomplete \iffalse).

Is there a way to make this sectioning feature work in reledpar? An alternate solution through titlesec and titletoc may be possible, but it would be more complex.

MWE:

\documentclass{article}
\usepackage{reledmac, reledpar}
\begin{document}
\tableofcontents
\begin{pages}
\begin{Leftside}
\beginnumbering
%% the line below gives an error Argument of \ttl@straight@i has an extra }
%% (error even if the right side too has differentiated TOC and body section names to match these)
%\pstart[\section[Left section in TOC]{Left section in body}]
\pstart[\section{Left section}]
Left paragraph.
\pend
\endnumbering
\end{Leftside}
\begin{Rightside}
\beginnumbering
\pstart[\section{Right section}]
Right paragraph.
\pend
\endnumbering
\end{Rightside}
\end{pages}
\Pages

%\beginnumbering
%% the line below gives an error Incomplete \iffalse
%  \pstart[\section[Reledmac section in TOC]{Reledmac section in body}]
%    A reledmac paragraph.
%  \pend
%\endnumbering

% no error outside of reledpar and reledmac
\section[Non-reledpar section in TOC]{Non-reledpar section in body}
\end{document}

• titlesec, titletoc and tocloft, in one file? That's a pretty combination ;-) – user31729 Jan 12 at 15:11
• Oops! tocloft must have stuck when copied from somewhere else. I was experimenting with the other two, but they're not necessary either for this MWE, so I've removed them. Thanks. – fvogel Jan 12 at 15:36

It is a problem of expansion. I have notime now to understand the problem in reledmac code (you could open an issue), but a \unexpanded work around.

\documentclass{article}
\usepackage{reledmac, reledpar}
\begin{document}
\tableofcontents
\beginnumbering
\pstart[\unexpanded{\section[reledmac section in toc]{reledmac section in body}}]
a reledmac paragraph.
\pend
\endnumbering

% no error outside of reledpar and reledmac
\section[Non-reledpar section in TOC]{Non-reledpar section in body}
\end{document}