Screensaver lock screen incomplete and doesn't work properly for mult-head setup.

[Kent Lion]

After upgrading to 20.04 on a dual monitor setup using multi-head settings for each monitor, when I boot, the wallpaper defined for each screen is properly displayed. When I log on, the wallpaper defined for each screen is properly displayed in each workspace. However, when the screensaver kicks in, the lock screen only uses the wallpaper from the (portrait oriented) primary monitor, which doesn't fit too well on the landscape oriented secondary monitor. Never had that problem in 18.04, so I'm guessing the problem is that multi-head considerations were forgotten when the screensaver was separated from the power manager for 20.04. I don't know what package the screensaver is part of.

Also, on the 18.04 startup login screen and screensaver lock screens, moving the mouse between monitors causes the login dialog to move to the screen that the mouse cursor is on. This does not occur with the 20.04 screensaver lock screen, though it does occur with the login screens, so that's either an omission or a bug in the screensaver.

To reproduce the bug(s)/problems, on a dual monitor system set up so that each monitor displays a different wallpaper when logged on and logged off, and also from each other and in all workspaces, set the screensaver to lock after 5 minutes or less and let it lock with the mouse cursor left on the primary screen and then again with the mouse cursor left on the secondary screen.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubuntu-release-upgrader-core 1:20.04.28
ProcVersionSignature: Ubuntu 5.4.0-52.57-generic 5.4.65
Uname: Linux 5.4.0-52-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.9
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
CurrentDesktop: XFCE
Date: Wed Oct 21 13:07:21 2020
InstallationDate: Installed on 2019-11-29 (327 days ago)
InstallationMedia: Xubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: dist-upgrade
UpgradeStatus: Upgraded to focal on 2020-10-20 (1 days ago)
VarLogDistupgradeXorgFixuplog:
 INFO:root:/usr/bin/do-release-upgrade running
 INFO:root:No xorg.conf, exiting