In my setup, I make non-focused windows semi-transparent (using Xmonad
and its compose support).  This used to work perfectly, but with the
recent-ish update of emacs from 28.2 to 29.1, this broke.  (Basically,
what's described on
https://hackage.haskell.org/package/xmonad-contrib-0.16/docs/XMonad-Hooks-FadeInactive.html)

I've bisected this down to:

commit b299f173490f5c51476ad3c8436b19bb091c1b00
Author: Po Lu <luangruo@yahoo.com>
Date:   Tue May 10 09:32:59 2022 +0800

    Update alpha frame parameter when the window manager changes it

    * src/xfns.c (x_set_alpha): New function.  Set
    `alpha_identical_p' flag.
    (x_frame_parm_handlers): Use it to handle `alpha' instead.

    * src/xterm.c (x_set_frame_alpha): Make tests against current
    alpha safer.
    (handle_one_xevent): Set frame alpha when alpha property
    changes.
    * src/xterm.h (struct x_output): New flag `alpha_identical_p'.

 src/xfns.c  | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 src/xterm.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
 src/xterm.h |  4 ++++
 3 files changed, 108 insertions(+), 3 deletions(-)

which seems like a plausible change for causing such a bug.

Note that the transparency of the window corrects itself if there's a
message in the minibuffer, so it seems like emacs isn't always picking
up the change in transparency which happens as it is being focused.

Hello Tollef,

Please M-x report-emacs-bug to send this upstream.

]] Sean Whitton

Done.

One additional detail is I only see this with the nvidia X11 driver, not
with Intel.