bug#20607: 24.5; Problem with overlays at same position but in different windows

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 18 May 2015 21:59:26 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 20607@debbugs.gnu.org
> 
> > From: Oleh Krehel <ohwoeowho@gmail.com>
> > Date: Mon, 18 May 2015 20:29:10 +0200
> > 
> > 
> > Suppose I have two windows, WND1 and WND2, both displaying the same
> > buffer. In WND1, there's an overlay from 1 to 2 with window property
> > WND1 and display "ab". In WND2, there's an overlay from 1 to 3 with
> > window property WND2 and display "abc".
> > 
> > Instead of the expected, I see "ab" in WND1, but "abcabc" in WND2.  When
> > I `move-overlay' in the first window to 1-3, the glitch disappears, but
> > I actually want the overlay to be 1-2, not 1-3. If I have to make it
> > 1-3, I'd have to modify the display as well to include one more
> > character from the buffer. I think it's better to fix the overlay logic
> > rather than go for this work-around.
> 
> Please show the code to reproduce this.

Actually, you need not bother: I see it here.

For now, all I can say is that this is very old: Emacs 22 already
behaves like that.  I think the problem is that the display engine
bumps into the same overlay twice while walking the buffer, but I need
to take a closer look to be sure.