bug#14582: 24.3.50.1; Strange overlay behavior, when window-start is inside an overlay.

[Michael Heerdegen]

Eli Zaretskii <eliz@gnu.org> writes:

> Neither do I, so there's something else at work here.

I failed to find a recipe in half an hour and gave up for now - instead
I found one for a very similar case of unexpected auto-scrolling that
only appears when the new feature is turned on.  Also seems to depend on
the buffer contents.  Maybe it is related and a fix fixes the other
thing, too.

emacs -Q
1 C-h i
2 move point to the beginning of one of the last visible lines.
  no scrolling happens (good).
3 M-: (setq make-window-start-visible t) RET  => *info* buffer scrolled

If you scroll back so that (point-min) becomes visible and repeat step
2 any activation of the minibuffer, e.g. just hitting M-: or C-x k,
scrolls the *info* buffer.

Doesn't happen in C-h n.  Dunno what makes the difference - the fact
that *info* is narrowed or that different fonts are used.

Ah - wait, now I can reproduce the other thing, too:

M-:
(progn
  (setq-default display-time-interval 1.)
  (setq display-time-format "%H:%M:%S")
  (setq-default make-window-start-visible t)
  (display-time-mode +1))
RET
C-h i
[down] [down] not too fast ... until it scrolls

I guess it's the same and just differs in when and how redisplay is
triggered.

Michael.