Difficulty setting up multimonitor with fractional scaling

[Joe Barnett]

I've enabled fractional scaling and set my laptop's 3840x2160 screen to 175% scaling. Upon plugging in an external 1920x1080 monitor, my laptop's screen resets to 200% scaling, and the external screen is set to 100%, to the right of my laptop's screen.

If I try to set the laptop screen back to 175%, the Displays panel does not allow me to Apply, and journalctl outputs: Config not applicable: GDBus.Error:org.freedesktop.DBus.Error.InvalidArgs: Logical monitors not adjecent

Putting the external screen on the left or top of the laptop screen allows Apply to work (bottom or right does not work), but immediately reverts to the auto-set settings (200% laptop with 100% external on the right) and then clicking "revert" on the "revert or keep" dialog sets things to the requested scale factor and position (175% laptop with 100% external on the top/left).

I've also seen the settings randomly reset to 200% laptop with 100% external on the right upon doing things like clicking reply in evolution to open up a new compose window.

That's a bit long winded, so here's a shorter rundown of bugs description:
1) Upon connecting an external screen, the laptop screen scaling changes
2) Can't set external screen to the bottom or right of laptop screen with fractional scaling
3) Upon Application, the requested settings are reverted, and then reverting the reversion applies them, while "keeping" the change reverts
4) Certain random actions appear to reset to the undesired settings

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: mutter 3.30.0-4
ProcVersionSignature: Ubuntu 4.18.0-7.8-generic 4.18.5
Uname: Linux 4.18.0-7-generic x86_64
ApportVersion: 2.20.10-0ubuntu11
Architecture: amd64
CurrentDesktop: GNOME
Date: Wed Oct 3 15:17:03 2018
InstallationDate: Installed on 2018-09-26 (7 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: mutter
UpgradeStatus: Upgraded to cosmic on 2018-09-28 (5 days ago)

[Launchpad Janitor (janitor)]

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

[Daniel van Vugt (vanvugt)]

Thank you for reporting this bug to Ubuntu.
Ubuntu 18.10 (cosmic) reached end-of-life on July 18, 2019.

See this document for currently supported Ubuntu releases:
https://wiki.ubuntu.com/Releases

We appreciate that this bug may be old and you might not be interested in discussing it any more. But if you are then please upgrade to the latest Ubuntu version and re-test. If you then find the bug is still present in the newer Ubuntu version, please add a comment here telling us which new version it is in and change the bug status to Confirmed.