time-admin window doesn't install ntp when prompted

I'm using Xubuntu 17.04 but I don't think this problem is specific to Xubuntu.

By default, "Configuration" in "Time and Date Settings" is set to "Manual". If I change the option to "Keep synchronized with Internet servers" I am prompted to "Install NTP support" or to cancel the change. Obviously this is only when the ntp package isn't already installed.

Clicking on "Install NTP support" displays a notification window to say that an application is requesting additional packages and that is can be found in "Software". Clicking on that window brings up gnome-software which says that the requested package cannot be found.

I'm sure that in the past I was prompted for my administrator password as would be expected when installing software.

Recent updates have changed what is seen after asking for ntp to be installed.

*UPDATE*

For Xubuntu, the expected dialogs appear and ntp is installed.

For Lubuntu, an error message is now displayed:

*Could not install package*

GDBus.Error:org.freedekstop.org.DBus.Error.ServiceUnknown: the name org.freedesktop.PackageKit was not provided by an service files

ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: gnome-system-tools 3.0.0-4ubuntu3
ProcVersionSignature: Ubuntu 4.10.0-8.10-generic 4.10.0-rc8
Uname: Linux 4.10.0-8-generic x86_64
ApportVersion: 2.20.4-0ubuntu2
Architecture: amd64
CasperVersion: 1.380
CurrentDesktop: XFCE
Date: Wed Feb 22 15:16:50 2017
ExecutablePath: /usr/bin/time-admin
LiveMediaBuild: Xubuntu 17.04 "Zesty Zapus" - Alpha amd64 (20170222)
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-system-tools
UpgradeStatus: No upgrade log present (probably fresh install)