I found a discussion of this bug at https://askubuntu.com/questions/886593/alt-f4-switches-to-tty4 and a workaround (kbd_mode -s). No clue to what gets it in the wrong mode to begin with, though.
-- You received this bug notification because you are a member of Desktop Packages, which is subscribed to xorg-server in Ubuntu. https://bugs.launchpad.net/bugs/1791493 Title: Unwanted VT switch from alt + arrow keys Status in xorg-server package in Ubuntu: New Bug description: Recently the VT switching shortcut keys changed from ctrl+alt+arrowkeys and ctrl+alt+F-keys to just alt+arrowkeys/f-keys. This conflicts with many application keybindings, such as Firefox history back/forward. I don't know which package is to blame, xorg-server is my best guess. ProblemType: Bug DistroRelease: Ubuntu 18.04 Package: xserver-xorg-core 2:1.19.6-1ubuntu4 ProcVersionSignature: Ubuntu 4.15.0-33.36-generic 4.15.18 Uname: Linux 4.15.0-33-generic x86_64 .tmp.unity_support_test.0: ApportVersion: 2.20.9-0ubuntu7.2 Architecture: amd64 CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins' CompositorRunning: None CurrentDesktop: ubuntu:GNOME Date: Sun Sep 9 12:29:24 2018 DistUpgraded: 2018-08-23 19:06:02,004 DEBUG package 'libwebkit2gtk-4.0-37-gtk2' has unwanted removals, skipping DistroCodename: bionic DistroVariant: ubuntu ExtraDebuggingInterest: Yes GraphicsCard: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller [8086:0126] (rev 09) (prog-if 00 [VGA controller]) Subsystem: Lenovo 2nd Generation Core Processor Family Integrated Graphics Controller [17aa:21da] InstallationDate: Installed on 2015-04-23 (1234 days ago) InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1) MachineType: LENOVO 4291Y2S ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-33-generic root=UUID=c7819f92-db3d-4e27-b7fa-297cdcda1875 ro quiet splash vt.handoff=1 SourcePackage: xorg-server UpgradeStatus: Upgraded to bionic on 2018-08-23 (16 days ago) dmi.bios.date: 05/13/2011 dmi.bios.vendor: LENOVO dmi.bios.version: 8DET45WW (1.15 ) dmi.board.asset.tag: Not Available dmi.board.name: 4291Y2S dmi.board.vendor: LENOVO dmi.board.version: Not Available dmi.chassis.asset.tag: E1YZD dmi.chassis.type: 10 dmi.chassis.vendor: LENOVO dmi.chassis.version: Not Available dmi.modalias: dmi:bvnLENOVO:bvr8DET45WW(1.15):bd05/13/2011:svnLENOVO:pn4291Y2S:pvrThinkPadX220:rvnLENOVO:rn4291Y2S:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable: dmi.product.family: ThinkPad X220 dmi.product.name: 4291Y2S dmi.product.version: ThinkPad X220 dmi.sys.vendor: LENOVO version.compiz: compiz 1:0.9.13.1+18.04.20180302-0ubuntu1 version.libdrm2: libdrm2 2.4.91-2 version.libgl1-mesa-dri: libgl1-mesa-dri 18.0.5-0ubuntu0~18.04.1 version.libgl1-mesa-glx: libgl1-mesa-glx 18.0.5-0ubuntu0~18.04.1 version.xserver-xorg-core: xserver-xorg-core 2:1.19.6-1ubuntu4 version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.5-1ubuntu1 version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:18.0.1-1 version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20171229-1 version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.15-2 xserver.bootTime: Thu Aug 23 17:40:20 2018 xserver.configfile: default xserver.errors: Failed to load module "fbdev" (module does not exist, 0) Failed to load module "vesa" (module does not exist, 0) Failed to load module "fbdev" (module does not exist, 0) Failed to load module "vesa" (module does not exist, 0) xserver.logfile: /var/log/Xorg.0.log xserver.outputs: product id 4204 vendor AUO xserver.version: 2:1.18.4-0ubuntu0.8 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1791493/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp