Display scaling doesn't actually update display scale-factor

[Karl]

In the "Displays" GUI, there's a slider called "Scale for menu and title bars" that seems to update the scale-factor parameter (/com/ubuntu/user-interface/scale-factor). When I click and drag the slider around, it updates the screen's scale factor (most of the time). However, when I click the slider, then change the value with the left and right arrow keys, the scale-factor parameter is unchanged. Clicking "Apply" doesn't help.
I expected the slider to behave the same whether it was moved by mouse drags or keyboard movements.

Steps to replicate:
1. Open a terminal and run `dconf watch /com/ubuntu/user-interface/scale-factor`
2. Open the Displays GUI
3. Click the "Scale for menu and title bars" slider and move it around with the arrow keys. Note that the scale-factor in the terminal did not update.
4. Click "Apply". Note that the window is not rescaled.

I've also had trouble with mouse drags not updating scale-factor, but I'm having trouble replicating that issue.

As a side comment, it seems that the name "Scale for menu and title bars" is a little misleading. It controls the whole screen scaling, not just menu and title bars, yes?

I'm running the latest stable versions, Ubuntu 17.04 and unity-control-center 15.04.0+17.04.20170402.6-0ubuntu1

ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: unity-control-center 15.04.0+17.04.20170402.6-0ubuntu1
ProcVersionSignature: Ubuntu 4.10.0-32.36-generic 4.10.17
Uname: Linux 4.10.0-32-generic x86_64
NonfreeKernelModules: zfs zunicode zavl zcommon znvpair
ApportVersion: 2.20.4-0ubuntu4.5
Architecture: amd64
CurrentDesktop: Unity:Unity7
Date: Sat Aug 26 12:38:45 2017
InstallationDate: Installed on 2016-01-09 (595 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
ProcEnviron:
 LANGUAGE=en_US
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: unity-control-center
UpgradeStatus: Upgraded to zesty on 2017-04-18 (130 days ago)

[Khurshid Alam (khurshid-alam)]

Reproducible on artful.