Shell appears not to accepts ~/.emacs_bash?

[Colin Baxter <m43cap@yandex.com>]

On GNU Emacs 27.0.50 (build 1, i686-pc-linux-gnu, GTK+ Version 3.14.5)
of 2019-04-10.

1. No ~/.emacs_bash file present.
2. src/emacs -q <RET>.
3. M-x shell <RET>.
4. Output is satisfactory.
5. Touch ~/.emacs_bash.
6. Repeat 2., 3.
7. Output is satisfactory.
8. Edit ~/.emacs_bash and add a comment #, but no further character or
white space. Save file.
9. Repeat 2., 3.
10. Shell output now has two prompts in one single line of the form
`username@host:~/git/emacs'.
11. Further additions to ~/.emacs_bash produce further prompts, at the
rate it seems of one prompt per line in ~/.emacs_bash.

I think this is fairly new behaviour (within days, or a week or two) and
does not occur with emacs-26.1. I cannot find anything relevant in NEWS,
at least not that I understand.

I am on 3.16.0-8-686-pae #1 SMP Debian 3.16.64-2 (2019-04-01) i686 GNU/Linux.

Best wishes,

-- 
Colin Baxter
m43cap@yandex.com