Show side by side view of changes does nothing

[Anders Magnus Andersen]

In the update process I was notified that GRUB was changed (not the path name /etc/default/grub) just GRUB. I choose the option to view a side by side comparison.

The updater just moved on and kept my changed file. Nothing opened, no warnings, it just moved on.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: update-manager 1:18.04.11.4
ProcVersionSignature: Ubuntu 4.15.0-29.31-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: communitheme:ubuntu:GNOME
Date: Tue Jul 24 23:10:21 2018
GsettingsChanges:
 b'com.ubuntu.update-manager' b'show-details' b'true'
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'window-width' b'645'
 b'com.ubuntu.update-manager' b'launch-time' b'int64 1532466529'
InstallationDate: Installed on 2018-06-30 (23 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)