Failed to poweroff system with session menu by selecting poweroff option with arrow key

[Po-Hsu Lin]

Steps:
1. Install Yakkety, boot to desktop, dist-upgrade to the latest state.
2. Press the power button to bring up the session menu, select the "poweroff" option with left arrow key and hit enter.

Expected result:
 - System should poweroff normally.

Actual result:
 - Session menu closed but nothing happened. Tested with -updates and -proposed, they're all the same.

Attachment is a recording for this issue.
Please note that this issue is not 100% reproducible, sometimes even selecting poweroff option with mouse click will fail too. And it's only limit to the poweroff option.

Poweroff action via the menu brings up by the "Shutdown" option from the cog wheel in the upper-right corner works fine.

Error log could be found in syslog:
Jan 5 23:47:28 ubuntu-Latitude-7370 unity-settings-[1485]: Failed to call Shutdown on session manager: GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._g_2dio_2derror_2dquark.Code19: Operation was cancelled

More complete log:
Jan 5 23:47:25 ubuntu-Latitude-7370 gnome-session[1498]: gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:25 ubuntu-Latitude-7370 gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:25 ubuntu-Latitude-7370 gnome-session[1498]: gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:25 ubuntu-Latitude-7370 gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:25 ubuntu-Latitude-7370 gnome-session[1498]: gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:25 ubuntu-Latitude-7370 gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:26 ubuntu-Latitude-7370 gnome-session[1498]: gnome-session-binary[1498]: WARNING: Client '/org/gnome/SessionManager/Client1' failed to reply before timeout
Jan 5 23:47:26 ubuntu-Latitude-7370 gnome-session-binary[1498]: WARNING: Client '/org/gnome/SessionManager/Client1' failed to reply before timeout
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session-binary[1498]: Entering running state
Jan 5 23:47:28 ubuntu-Latitude-7370 unity-settings-[1485]: Failed to call Shutdown on session manager: GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._g_2dio_2derror_2dquark.Code19: Operation was cancelled
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session[1498]: gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session[1498]: gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session[1498]: gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session[1498]: gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session[1498]: gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session-binary[1498]: GLib-GObject-CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Jan 5 23:47:28 ubuntu-Latitude-7370 gnome-session-binary[1498]: Entering running state
Jan 5 23:47:28 ubuntu-Latitude-7370 unity-panel-ser[1612]: menus_destroyed: assertion 'IS_WINDOW_MENU(wm)' failed

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: unity 7.5.0+16.10.20161112-0ubuntu1
ProcVersionSignature: Ubuntu 4.8.0-34.36-generic 4.8.11
Uname: Linux 4.8.0-34-generic x86_64
.tmp.unity_support_test.0:

ApportVersion: 2.20.3-0ubuntu8.2
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Thu Jan 5 23:44:34 2017
DistUpgraded: Fresh install
DistroCodename: yakkety
DistroVariant: ubuntu
GraphicsCard:
 Intel Corporation HD Graphics 515 [8086:191e] (rev 07) (prog-if 00 [VGA controller])
   Subsystem: Dell HD Graphics 515 [1028:071b]
InstallationDate: Installed on 2017-01-06 (0 days ago)
InstallationMedia: Ubuntu 16.10 "Yakkety Yak" - Release amd64 (20161012.2)
MachineType: Dell Inc. Latitude 7370
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.8.0-34-generic.efi.signed root=UUID=24624713-9336-4ae2-bf4a-e84906f0a72a ro quiet splash vt.handoff=7
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/31/2016
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.9.3
dmi.board.vendor: Dell Inc.
dmi.chassis.type: 9
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr1.9.3:bd10/31/2016:svnDellInc.:pnLatitude7370:pvr:rvnDellInc.:rn:rvr:cvnDellInc.:ct9:cvr:
dmi.product.name: Latitude 7370
dmi.sys.vendor: Dell Inc.
version.compiz: compiz 1:0.9.13.0+16.10.20160818.2-0ubuntu2
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.70-1
version.libgl1-mesa-dri: libgl1-mesa-dri 12.0.3-1ubuntu2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 12.0.3-1ubuntu2
version.xserver-xorg-core: xserver-xorg-core 2:1.18.4-1ubuntu6.1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.2-1ubuntu1
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.7.1-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20160706-1ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.12-2
xserver.bootTime: Thu Jan 5 23:38:58 2017
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.18.4-1ubuntu6.1
xserver.video_driver: modeset

[Launchpad Janitor (janitor)]

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

[Alberto Salvia Novella (es20490446e)]

Likely related with:
(https://bugzilla.gnome.org/show_bug.cgi?id=643457#c137)

[dino99 (9d9)]

This is an unsupported release now. Please think to install the next LTS 'Bionic 18.04'

http://cdimage.ubuntu.com/ubuntu-next/daily-live/current/
https://www.omgubuntu.co.uk/2018/02/ubuntu-18-04-minimal-install-option