Great, thanks!

Only you can find this quickly.

Fabtice

Le mar. 21 janv. 2020 à 17:32, Eli Zaretskii <eliz@gnu.org> a écrit :

> > From: Fabrice Popineau <fabrice.popineau@gmail.com>
> > Date: Mon, 20 Jan 2020 19:41:48 +0100
> > Cc: 39188@debbugs.gnu.org
> >
> > Maybe it is not the most important bug (except if Windows start to tell
> > emacs that there are screen readers everywhere)
>
> I found the problem.  As part of redisplay, we sometimes scroll
> rectangular portions of the window, as pixels, up and down.  When we
> do so, we first turn off the cursor, but when the system caret is used
> instead of the cursor, we hide and unhide the caret in a separate UI
> thread.  So there's a race between the main thread which scrolls the
> pixels and the UI thread that draws the caret, and that race causes
> the pixels of the caret to sometimes be copied with the rectangular
> area that is scrolled.
>
> The solution is to disable the scrolling in w32_scroll_run when the
> system caret is in use.  This slows down redisplay to some extent
> (because w32_scroll_run is a redisplay optimization), but I don't see
> any easy way around that.
>
> Should be fixed now on the emacs-27 branch.
>