User-defined marks swallowed if inside multicols

[cspiel]

Brief outline of the bug

I find that even with the latest (released) multicol.sty, v1.9h,
user-defined marks are recorded as proven by the log file but
they do not quite make it to \FirstMark or \LastMark if the
insertion points are within a multicols environment.

Otherwise the \NewMarkClass mechanism works flawlessly.

In the example given below I'd expect the head to show a-n,
however what I get is a-b.

The problem may share a distant relationship with issue #1130.

Minimal example showing the bug

\RequirePackage{latexbug}
\documentclass{article}

\usepackage{multicol}

\NewMarkClass{DictMark}
\DebugMarksOn

\makeatletter
\def\@oddhead{\FirstMark{DictMark}--\LastMark{DictMark}\hfill\thepage}
\let\@evenhead=\@oddhead
\makeatother

\begin{document}
\InsertMark{DictMark}{a}a
\InsertMark{DictMark}{b}b

\begin{multicols}{2}
\InsertMark{DictMark}{m}m
\InsertMark{DictMark}{n}n
\end{multicols}

%%--\InsertMark{DictMark}{z}z
\end{document}

Log file (required) and possibly PDF file

l3marks.log
l3marks.pdf

[FrankMittelbach]

The problem is that multicol is still not yet enabled to support the new mark mechanism. I'm aware of that but haven't found the time to address this.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity.