Hi Berthold, thanks for the report.

>>>>> Berthold Lorke <berthold@lorke.de> writes:
> Okay, I am sorry if I am bugging you (no pun intended), but I now
> still do believe there is a problem.

> I am using auctex 13.1.9.  Let us assume the following inside of a
> buffer in `tex-mode` with auctex installed.  I did this with a fresh
> Emacs, no other packages installed and no config.

I assume AUCTeX latex mode, not `tex-mode`.

> - Mark the region where I wrote `a^2 + b^2 = c^2`, that is line 7.
> - Perform `M-x LaTeX-environment`, put `equation` in the prompt, press
>   enter, and then for the next prompt press enter again.

[...]

> As you can see, it is not correctly indented.  Have tried this
> multiple times on multiple machines and so on.  Can you confirm this
> behaviour?

Indeed. This is't nice. :-(

Currenty, `LaTeX-insert-environment' doesn't indent the active region if
the environment is in `LaTeX-indent-environment-list'. I expect that it
doesn't harm if it indents. Could you try the attached patch?

Bye,
Ikumi Keita
#StandWithUkraine #StopWarInUkraine