Comment 0 for bug 1768613

"Displays" in the Gnome Control Center doesn't seem to be working.
When I connect an external monitor (Dell P2415Qb) to my laptop (XPS 13 touch screen), most of the "Join Displays" options do not work: when I click "Apply" after changing resolution or display arrangement, the external monitor goes to sleep. When I move the mouse into the region that the monitor should be, it seems to go into that region--it feels like although the laptop knows that the monitor is there, the monitor doesn't get a signal.
The only permutation (besides setting display mode to "Mirror") that I have found to work (i.e. the external monitor doesn't go to sleep) involves setting the resolution to 1600x900 on both the laptop screen and the monitor. This only works when the monitor is to the left of the screen like so:
-------------------
| 1 | 2 |
| | |
| | |
-------------------
When I try to put display 2 (the monitor) above display 1, or of course change resolution, the monitor goes to sleep.

I would expect that any permutation of screen positions and resolutions that is allowed by the GUI would work, i.e. the external monitor should not go to sleep after applying changes when "Join Displays" is selected. It's odd that only 1600x900 is allowed (both the laptop screen and external monitor can do much better), and that the relative positions of the screens makes a difference.

Ubuntu 18.04

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnome-control-center 1:3.28.1-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
Uname: Linux 4.15.0-20-generic x86_64
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed May 2 11:15:56 2018
InstallationDate: Installed on 2018-04-27 (5 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-control-center
UpgradeStatus: No upgrade log present (probably fresh install)