Logout always asks about rebooting to finish installing updates

[D Tangman]

I am logged into a gnome-flashback compiz session. When I click on the icon in the upper right corner of the screen and select "Log Out..." from the resulting menu, I always get a dialog with the following content:

    Are you sure you want to close all programs and log out?
    Some software updates won't be applied until the computer next restarts.

It doesn't seem to matter how many times I reboot the system, this dialog is always presented on logout. If I switch back to a default Ubuntu session (Unity? I'm doing this from memory, so all I can say for certain is that it's the choice that isn't one of the flashback options) I get a dialog that asks me if I'm sure I want to log out, with options to log out or to lock the screen and no mention of needing to finish installing software updates.

I have looked at the code in indicator-session/src/backend-dbus/actions.c, where this message is generated, and have been unable to determine what condition would allow a flashback session to log out without producing the dialogue shown above.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: indicator-session 12.10.5+16.04.20160412-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-38.57-generic 4.4.19
Uname: Linux 4.4.0-38-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CurrentDesktop: GNOME-Flashback:Unity
Date: Mon Oct 3 18:06:04 2016
InstallationDate: Installed on 2016-08-29 (35 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
SourcePackage: indicator-session
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

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

[Dane Maslen (dane-maslen)]

I also see this behaviour. I use Metacity for my login session.