Subject: bug#58176: 29.0.50; mouse-set-point region flicker with highlight-nonselected-windows=t and same buffer in two windows

From: Eli Zaretskii <[email-masked]>
Date: Thu, 29 Sep 2022 21:54:03 +0300

> Date: Thu, 29 Sep 2022 19:38:28 +0200
> From: miha--- via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <[email-masked]>
> 
> 1. (setq highlight-nonselected-windows t)
> 2. 'C-x 2'
> 3. Click with mouse-1 somewhere to move point
> 
> Notice that for the duration mouse-1 being held down for the click,
> region highlighting appears in the non-selected window. Usually the
> click is short so the region only appears for a short time, which can be
> perceived as a somewhat annoying flicker.

It's a direct consequence of the fact that point is different in each
window.  I don't see any bug here, FWIW.  If you don't like this side
effect of highlight-nonselected-windows, then don't set it non-nil.