Keyboard 'alternative switch to next source' layout option is not honoured by X applications run by XWayland

[LGB [Gábor Lénárt]]

I have "Alternative switch to next source" option set to "Right Alt (while pressed)" in "Input source options" within "Region & Language" in settings. I use US kbd layout, but often I need my national characters, so I use the "while pressed" solution since years, it's much faster than always changing KBD layouts. Now, in Ubuntu 17.10 this still works perfectly in applications like gnome-terminal. However I have the suspect it never works now in any X applications (like: firefox, xterm, and few of them what I've tried). So I have the feeling that "legacy" X apps run by Xwayland does not honour the input settings properly, which is a problem for me to using the desktop now in this form. Surely, it is only my guess that it's the problem of Xwayland now, what runs the X apps on "top of" wayland.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: xwayland 2:1.19.5-0ubuntu2
ProcVersionSignature: Ubuntu 4.13.0-16.19-generic 4.13.4
Uname: Linux 4.13.0-16-generic x86_64
ApportVersion: 2.20.7-0ubuntu3
Architecture: amd64
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Tue Oct 17 20:12:31 2017
DistUpgraded: 2017-06-20 12:44:34,135 DEBUG Running PostInstallScript: './xorg_fix_proprietary.py'
DistroCodename: artful
DistroVariant: ubuntu
DkmsStatus:
 virtualbox, 5.1.28, 4.13.0-15-generic, x86_64: installed
 virtualbox, 5.1.28, 4.13.0-16-generic, x86_64: installed
ExtraDebuggingInterest: Yes
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] Richland [Radeon HD 8470D] [1002:9996] (prog-if 00 [VGA controller])
   Subsystem: ASRock Incorporation Richland [Radeon HD 8470D] [1849:9996]
InstallationDate: Installed on 2015-07-10 (829 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release i386 (20150422)
MachineType: To Be Filled By O.E.M. To Be Filled By O.E.M.
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.13.0-16-generic root=UUID=d203063e-78c0-425a-bee2-0e3ecb4ea74c ro quiet splash scsi_mod.use_blk_mq=1 vt.handoff=7
SourcePackage: xorg-server
UpgradeStatus: Upgraded to artful on 2017-06-20 (119 days ago)
dmi.bios.date: 02/05/2016
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: P2.90
dmi.board.name: FM2A88M Extreme4+
dmi.board.vendor: ASRock
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP2.90:bd02/05/2016:svnToBeFilledByO.E.M.:pnToBeFilledByO.E.M.:pvrToBeFilledByO.E.M.:rvnASRock:rnFM2A88MExtreme4+:rvr:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.family: To Be Filled By O.E.M.
dmi.product.name: To Be Filled By O.E.M.
dmi.product.version: To Be Filled By O.E.M.
dmi.sys.vendor: To Be Filled By O.E.M.
version.compiz: compiz 1:0.9.13.1+17.10.20170901-0ubuntu1
version.libdrm2: libdrm2 2.4.83-1
version.libgl1-mesa-dri: libgl1-mesa-dri 17.2.2-0ubuntu1
version.libgl1-mesa-glx: libgl1-mesa-glx 17.2.2-0ubuntu1
version.xserver-xorg-core: xserver-xorg-core 2:1.19.5-0ubuntu2
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.5-1ubuntu1
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.10.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20170309-0ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.15-2
xserver.bootTime: Wed Jun 21 14:44:53 2017
xserver.configfile: default
xserver.errors:

xserver.logfile: /var/log/Xorg.0.log
xserver.version: 2:1.19.3-1ubuntu1
xserver.video_driver: radeon