(I think I sent this one prematurely once already; sorry.)

Glenn Morris <rgm@gnu.org> writes:

> This issue occurs since at least Emacs 21.1.
> If you have a non-empty ~/.emacs_bash file, eg one that contains just:
>
> #comment
>
> and do M-x shell with the bash shell, then you get an extra N copies of
> your prompt, as the N lines of ~/.emacs_bash are fed to the shell by
> comint-exec.

This bug is still present in Emacs 28, although it looks a bit different
now: