On Tue, 23 Jun 2020, Mattias Engdegård wrote:

> Thank you! This bug has been fixed in Emacs 27; see https://debbugs.gnu.org/cgi/bugreport.cgi?bug=38152 .

Thanks for the pointer.  I confirm that the patch in bug #38152 fixes the 
previous test case.  However the following slightly different test case 
still has a similar problem:

---- snip ----
\documentclass{article}
\begin{document}
\begin{environment}
   Some code % a comment
   More code
\end{environment}
\end{document}
---- snip ----

If you position point at the start of the line "  More code" and hit M-q, 
the result is

\begin{environment}
   Some code % a comment More code
\end{environment}

Should this bug #42016 be reopened or should I file a new bug?

-- 
Nate Eldredge
nate@thatsmathematics.com