Application menu of GTK apps is cut off when the window is resized and made smaller in Xorg sessions

[Vincenzo Tamborino Frisari]

1. When opening a text document (with standard text editor) or a pdf with "Pdf viewer" and clicking on the "menu" icon at the top right of the window, the menu shows up correctly.
2.If I resize the window making it shorter than the menu itself, I would expect the menu to remain fully visible or at least in some way graphically accessible (resized or scrollable).
3. Instead, I can no more see some options of the menu: a part of it is not visible (as it was graphically cut). So you can't see nor select with the mouse the non-visible part of the menu.
4. I noticed you can navigate and select the options (both visible or non-visible) of the menu using arrows and Enter from the keyboard. However this is not a solution because you still cannot see a part of the menu

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: xorg 1:7.7+19ubuntu14
ProcVersionSignature: Ubuntu 5.4.0-56.62-generic 5.4.73
Uname: Linux 5.4.0-56-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.13
Architecture: amd64
BootLog: Error: [Errno 13] Permission denied: '/var/log/boot.log'
CasperMD5CheckResult: skip
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Mon Dec 7 23:33:35 2020
DistUpgraded: 2020-12-01 09:42:59,803 ERROR got error from PostInstallScript ./xorg_fix_proprietary.py (g-exec-error-quark: Failed to execute child process “./xorg_fix_proprietary.py” (No such file or directory) (8))
DistroCodename: focal
DistroVariant: ubuntu
DkmsStatus:
 btusb, 4.0, 5.4.0-54-generic, x86_64: installed
 btusb, 4.0, 5.4.0-56-generic, x86_64: installed
 digimend, 10, 5.4.0-54-generic, x86_64: installed
 digimend, 10, 5.4.0-56-generic, x86_64: installed
 rtbth, 3.9.6, 5.4.0-56-generic, x86_64: installed
ExtraDebuggingInterest: Yes, if not too technical
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Sumo [Radeon HD 6620G] [1002:9641] (prog-if 00 [VGA controller])
   Subsystem: Toshiba Corporation Sumo [Radeon HD 6620G] [1179:fc52]
 Advanced Micro Devices, Inc. [AMD/ATI] Seymour [Radeon HD 6400M/7400M Series] [1002:6760] (prog-if 00 [VGA controller])
   Subsystem: Toshiba Corporation Radeon HD 7470M [1179:fc52]
InstallationDate: Installed on 2020-03-23 (259 days ago)
InstallationMedia: Ubuntu 18.04.4 LTS "Bionic Beaver" - Release amd64 (20200203.1)
MachineType: TOSHIBA SATELLITE L750D
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-56-generic root=/dev/mapper/ubuntu--vg-root ro quiet splash vt.handoff=7
SourcePackage: xorg
Symptom: display
UpgradeStatus: Upgraded to focal on 2020-12-01 (6 days ago)
dmi.bios.date: 11/23/2011
dmi.bios.vendor: Insyde Corp.
dmi.bios.version: 1.50
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: Torpedo
dmi.board.vendor: AMD
dmi.board.version: Base Board Version
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: AMD
dmi.chassis.version: None
dmi.modalias: dmi:bvnInsydeCorp.:bvr1.50:bd11/23/2011:svnTOSHIBA:pnSATELLITEL750D:pvrPSK36E-05P00LIT:rvnAMD:rnTorpedo:rvrBaseBoardVersion:cvnAMD:ct10:cvrNone:
dmi.product.family: Type1Family
dmi.product.name: SATELLITE L750D
dmi.product.sku: PSK36E-05P00LIT
dmi.product.version: PSK36E-05P00LIT
dmi.sys.vendor: TOSHIBA
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.101-2
version.libgl1-mesa-dri: libgl1-mesa-dri 20.0.8-0ubuntu1~20.04.1
version.libgl1-mesa-glx: libgl1-mesa-glx 20.0.8-0ubuntu1~20.04.1
version.xserver-xorg-core: xserver-xorg-core 2:1.20.8-2ubuntu2.6
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:19.1.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20200226-1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.16-1

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Daniel van Vugt (vanvugt)]

It appears the problem only happens in Xorg sessions, not Wayland sessions. And it happens with a bare Xorg server too, so it's not mutter/shell bug.