🚀 go-pugleaf

In GNU Emacs 19.25.1 of Thu Jun  2 1994 on penelope (sparc-sun-sunos4.1.3C)

Compiled with toolkit.

The value of (window-end) seems to be its previous value, immediately
after a `scroll-up'.

Start an emacs -q, and insert into *scratch*:

(defun bug-scroll-down (&optional arg)
  (interactive "P")
  (scroll-down arg)
  (message "%d to %d" (window-start) (window-end)))

(defun bug-scroll-up (&optional arg)
  (interactive "P")
  (scroll-up arg)
  (message "%d to %d" (window-start) (window-end)))

(define-key global-map "\M-v" 'bug-scroll-down)
(define-key global-map "\C-v" 'bug-scroll-up)

and then M-x eval-current-buffer RET, C-x C-f .../src/fileio.c RET, and
resize the frame to 80x40.

Try ESC ESC SPC (window-end) RET.  The minibuffer shows 1131.

Type C-v.  The message shown is "1119 to 1131".

Now try ESC ESC SPC (window-end) RET.  The minibuffer shows 1562.

If you M-x goto-char 1131 RET then you will be moved to the start of the
third line.  M-x goto-char 1562 RET will take you to the start of the line
following the last that is currently visible (correct, of course).

You can do C-v a few times; you will always find the message (window-end)
to be the start of the third line, i.e. the previous value of (window-end),
minibuffer (window-end) to be correct.  There is no problem with M-v.

Bizarre.  Simon.