'Details of updates' frame does not expand vertically

[PJSingh5000]

SUMMARY

There are two expandable sections of the Software Updater window:
  1. 'Details of updates'
  2. 'Technical description'

When the Software Updater window first opens, the 'Details of updates' section is not expand vertically, and an empty 'Technical description' takes 1/2 the vertical space.

ISSUE

When the Software Updater window first opens, these sections are given the same vertical height, even though 'Technical description' has not been expanded. As a result, 'Details of updates' takes 1/2 the vertical space, and 'Technical description' takes the other 1/2. However nothing is shown in the 'Technical description' section, so Software Updater has a large empty space at the bottom 1/2 of the window. This is especially pronounced if you increase the vertical height of the Software Updater window.

See the issue in the attached screenshot 'Software Updater With Bug.png'.

STEPS TO RECREATE

1. Open Software Updater when you have updates pending.
2. Notice that the 'Technical description' section is collapsed, so it does not display text.
3. Do _not_ click on the expander triangle next to 'Technical description'.
4. Stretch the Software Updater window vertically using the bottom or top window edge and mouse.
5. Notice that 'Technical description' area takes 1/2 of the vertical window space even though it has not been expanded. **THIS IS THE ISSUE***

6. Close the Software Updater window. (Do _not_ click Install Now).
7. Open Software Updater (when you have updates pending).
8. Notice that the window 'remembers' its previous size, and is stretched vertically.
9. Notice that 'Technical description' area still takes 1/2 of the vertical window space even though it has not been expanded. **THIS IS THE ISSUE***

10. Click on the expander triangle next to 'Technical description'
11. A text area appears below 'Technical description'. (It may be blank if you have not selected a package in the 'Details of updates' section, but this is OK).
12. Notice that 'Technical description' area takes 1/2 of the vertical window space, since it has been expanded. This is OK, because there ~is~ a text area to display.

13. Click on the expander triangle next to 'Technical description' again to collapse this section.
14. Notice that 'Technical description' now appears at the _bottom_ of the window. It no longer takes 1/2 the vertical space. The 'Details of updates' frame now uses most of the vertical space, as it should.
15. ***This is how the Software Updater window should look when it first opens in step 2 above.***

HOW IT SHOULD BEHAVE

When the Software Updater window first opens:
- The 'Technical description' section should be shown near the _bottom_ of the window.
- The 'Details of updates' section should be stretched to fill the available vertical space.
- The 'Technical description' section should not take 1/2 the vertical space.
- The 'Technical description' section should only use 1/2 the vertical space when it is expanded (using the the expander triangle).

See the the expected behavior in the attached screenshot 'Software Updater How It Should Look.png'.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: update-manager 1:18.04.11
ProcVersionSignature: Ubuntu 4.15.0-23.25-generic 4.15.18
Uname: Linux 4.15.0-23-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.9-0ubuntu7.2
Aptdaemon:

Architecture: amd64
CurrentDesktop: GNOME
Date: Tue Jun 26 08:51:21 2018
GsettingsChanges:
 b'com.ubuntu.update-manager' b'show-details' b'true'
 b'com.ubuntu.update-manager' b'window-height' b'948'
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'window-width' b'586'
 b'com.ubuntu.update-manager' b'launch-time' b'int64 1530011694'
InstallationDate: Installed on 2018-05-09 (48 days ago)
InstallationMedia: Ubuntu 18.04.0 2018.05.09 LTS x64 "Custom Bionic Beaver"
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)

[PJSingh5000 (pjsingh5000)]

Software Updater - How It Should Look

[Launchpad Janitor (janitor)]

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