Bug#1125273: Black screen flash during GDM to GNOME session transition after 13.3 upgrade

[ajmasia]

Package: mutter-common
Version: 48.7-0+deb13u1
Severity: normal
Tags: upstream
X-Debbugs-Cc: ajmasia.dev at ysnp.link

After upgrading from Debian 13.2 to 13.3, the transition from GDM to the
GNOME session shows a momentary black screen (flash) instead of the
smooth animation that existed before.

* What led up to the situation?
Upgraded from Debian 13.2 to 13.3 (released January 10th, 2026) which
includes mutter and gnome-shell "bugfix releases".

* What exactly did you do (or not do) that was effective (or ineffective)?
Simply logged in via GDM after the upgrade.

* What was the outcome of this action?
Screen goes black for a moment, then the GNOME session appears abruptly.

* What outcome did you expect instead?
Smooth animated transition from GDM greeter to the desktop session,
as it worked in Debian 13.2.

Additional information:
- Reproducible on 2 different machines (desktop and laptop)
- Desktop GPU: AMD Phoenix3 (RDNA3 integrated graphics)
- This is a cosmetic regression, not a blocker

Versions:
mutter-common: 48.7-0+deb13u1
gnome-shell: 48.7-0+deb13u1
gdm3: 48.0-2


-- System Information:
Debian Release: 13.3
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.17.8+deb13-amd64 (SMP w/16 CPU threads; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages mutter-common depends on:
ii  dconf-gsettings-backend [gsettings-backend]  0.40.0-5

mutter-common recommends no packages.

mutter-common suggests no packages.

-- no debconf information