bug#45116: 26.3; refill-mode doesn't allow me to add text at the end of a paragraph

[Eli Zaretskii <eliz@gnu.org>]

> From: David Klein <dklein0@gmail.com>
> Date: Tue, 8 Dec 2020 10:16:40 +0200
> 
> runemacs.exe -Q
> (setq auto-mode-alist
>       (cons '("\\.latex$" . latex-mode) auto-mode-alist))^X^E
> (add-hook 'latex-mode-hook 'refill-mode)^X^E
> ^X^F junk.latex
> Type in a few random lines interspersed with empty lines
> Go back to the end of a line that is followed by an empty line and type
> a space (or several). No space gets inserted. Non whitespace inserts correctly.

Isn't that expected,, given that the doc string of this mode says:

                                             When enabled, the
  current paragraph is refilled as you edit.  Self-inserting
  characters only cause refilling if they would cause
  auto-filling.

"Refilled as you edit means excess whitespace is removed, no?