Public bug reported:
I am on Ubuntu 26.04, running the default wayland session (GNOME 50). I am not
sure if xorg is the correct package, but this is what the ubuntu-bug utility
prompted for "display".
Description: Ubuntu 26.04 LTS
Release: 26.04
I have two external displays connected, one 4K Koorui Monitor (model
number S2741LM) via USB-C (Thunderbolt 4 port), and one ASUS TUF 1440p
monitor which is set up vertically connected via HDMI. They are
connected to a Dell Pro 16 Plus laptop (PB16255).
The scaling on the 1440p monitor is 100%, then scaling on the 4K monitor
is 150%.
The problem:
I see a flashing line of pixels on the bottom of the 4K monitor when scaling is
higher than 125%. It looks like a reflection of the current window.
How I reproduce this:
(THIS ONLY HAPPENS SOMETIMES... But this is the main way that I can reproduce
this. I'm not sure what the initial conditions that trigger this are. It seems
that after I switch scaling, it fixes itself for a while)
I take any window and drag the window down so that the bottom of the window is
beyond the bottom of the display. The pixels of the window that cross over the
bottom edge of the screen get painted onto the bottom of the screen. When then
I maximize the window (and it is now fully back in view), I see that painted
line on the bottom row of pixels. It flickers, and if I change the content on
the window, I see the colour of this strip of pixels change.
NOTE:
1) I only am able to reproduce this on my 4K monitor. If I adjust the scaling
up on the 1440p monitor even to some large value like 250%, I still do not see
this effect.
2) I only see this happen on the bottom edge. No other edge gets "painted".
The expectation:
I expect not to see this flashing line of pixels.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: xorg (not installed)
ProcVersionSignature: Ubuntu 7.0.0-15.15-generic 7.0.0
Uname: Linux 7.0.0-15-generic x86_64
ApportVersion: 2.34.0-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Tue May 12 10:45:36 2026
InstallationDate: Installed on 2026-04-25 (17 days ago)
InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1)
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
XDG_RUNTIME_DIR=<set>
SourcePackage: xorg
Symptom: display
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: xorg (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug corruption resolute wayland-session
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https://bugs.launchpad.net/bugs/2152250
Title:
Window "paints" the bottom row of pixels on 4K monitor at scaling
higher than 125%.
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