Comment 9 for bug 1760818

Seems reinstalling ubuntu-desktop fixed it for real, ibus is now in GTK_IM_MODULE for new users.

Not sure which package in particular, but here's the apt history excerpt:

Start-Date: 2018-04-30 14:13:24
Commandline: apt install ubuntu-desktop
Requested-By: michal (1000)
Install: libreoffice-style-breeze:amd64 (1:6.0.3-0ubuntu1, automatic), gir1.2-geocodeglib-1.0:amd64 (3.25.4.1-4, automatic), fonts-tlwg-laksaman:amd64 (1:0.6.4-2, automatic), network-manager-pptp:amd64 (1.2.6-1, automatic), fonts-lao:amd64 (0.0.20060226-9ubuntu1, automatic), acpid:amd64 (1:2.0.28-1ubuntu1, automatic), hplip-data:amd64 (3.17.10+repack0-5, automatic), fonts-tlwg-purisa:amd64 (1:0.6.4-2, automatic), gnome-calendar:amd64 (3.28.1-1ubuntu2, automatic), libfwup1:amd64 (10-3, automatic), fonts-thai-tlwg:amd64 (1:0.6.4-2, automatic), gnome-video-effects:amd64 (0.4.3-1ubuntu1, automatic), printer-driver-splix:amd64 (2.0.0+svn315-6fakesync1, automatic), dc:amd64 (1.07.1-2, automatic), whoopsie:amd64 (0.2.62, automatic), gnome-control-center:amd64 (1:3.28.1-0ubuntu1, automatic), ifupdown:amd64 (0.8.17ubuntu1, automatic), printer-driver-c2esp:amd64 (27-4, automatic), mscompress:amd64 (0.4-3build1, automatic), app-install-data-partner:amd64 (16.04, automatic), bluez-cups:amd64 (5.48-0ubuntu3, automatic), fonts-tlwg-purisa-ttf:amd64 (1:0.6.4-2, automatic), printer-driver-hpcups:amd64 (3.17.10+repack0-5, automatic), fonts-tlwg-norasi:amd64 (1:0.6.4-2, automatic), vino:amd64 (3.22.0-3ubuntu1, automatic), apturl-common:amd64 (0.5.2ubuntu14, automatic), gnome-sudoku:amd64 (1:3.28.0-1, automatic), fonts-tlwg-typewriter-ttf:amd64 (1:0.6.4-2, automatic), laptop-detect:amd64 (0.16, automatic), fonts-tlwg-typist:amd64 (1:0.6.4-2, automatic), fonts-tlwg-norasi-ttf:amd64 (1:0.6.4-2, automatic), policykit-desktop-privileges:amd64 (0.20, automatic), libproxy1-plugin-gsettings:amd64 (0.4.15-1, automatic), printer-driver-foo2zjs:amd64 (20170320dfsg0-4, automatic), printer-driver-postscript-hp:amd64 (3.17.10+repack0-5, automatic), fonts-noto-cjk:amd64 (1:20170601+repack1-2, automatic), python3-reportlab-accel:amd64 (3.4.0-3build1, automatic), pptp-linux:amd64 (1.9.0+ds-2, automatic), fonts-tlwg-kinnari:amd64 (1:0.6.4-2, automatic), fonts-tlwg-mono:amd64 (1:0.6.4-2, automatic), ubuntu-desktop:amd64 (1.417), fonts-kacst-one:amd64 (5.0+svn11846-9, automatic), plymouth-label:amd64 (0.9.3-1ubuntu7, automatic), printer-driver-min12xxw:amd64 (0.0.9-10, automatic), printer-driver-pxljr:amd64 (1.4+repack0-5, automatic), gnome-mahjongg:amd64 (1:3.22.0-3, automatic), pppoeconf:amd64 (1.21ubuntu1, automatic), example-content:amd64 (50, automatic), fonts-tibetan-machine:amd64 (1.901b-5, automatic), libdazzle-1.0-0:amd64 (3.28.1-1, automatic), libqqwing2v5:amd64 (1.3.4-1.1, automatic), cheese:amd64 (3.28.0-1ubuntu1, automatic), fwupdate:amd64 (10-3, automatic), fonts-tlwg-typewriter:amd64 (1:0.6.4-2, automatic), memtest86+:amd64 (5.01-3ubuntu2, automatic), fonts-tlwg-garuda:amd64 (1:0.6.4-2, automatic), fonts-sil-abyssinica:amd64 (1.500-1, automatic), xcursor-themes:amd64 (1.0.4-1, automatic), ibus-gtk:amd64 (1.5.17-3ubuntu4, automatic), fonts-tlwg-kinnari-ttf:amd64 (1:0.6.4-2, automatic), python3-renderpm:amd64 (3.4.0-3build1, automatic), apturl:amd64 (0.5.2ubuntu14, automatic), deja-dup:amd64 (37.1-2fakesync1, automatic), aisleriot:amd64 (1:3.22.5-1, automatic), fonts-tlwg-waree:amd64 (1:0.6.4-2, automatic), gnome-font-viewer:amd64 (3.28.0-1, automatic), nautilus-share:amd64 (0.7.3-2ubuntu3, automatic), fonts-tlwg-typo:amd64 (1:0.6.4-2, automatic), libwmf0.2-7-gtk:amd64 (0.2.8.4-12, automatic), fonts-lklug-sinhala:amd64 (0.6-3, automatic), ppp:amd64 (2.4.7-2+2ubuntu1, automatic), libsmbios-c2:amd64 (2.4.1-1, automatic), branding-ubuntu:amd64 (0.10, automatic), ubuntu-software:amd64 (3.28.1-0ubuntu4, automatic), kerneloops:amd64 (0.12+git20140509-6ubuntu2, automatic), printer-driver-sag-gdi:amd64 (0.1-5, automatic), fonts-tlwg-sawasdee:amd64 (1:0.6.4-2, automatic), hplip:amd64 (3.17.10+repack0-5, automatic), fonts-tlwg-umpush:amd64 (1:0.6.4-2, automatic), guile-2.0-libs:amd64 (2.0.13+1-5build2, automatic), libhpmud0:amd64 (3.17.10+repack0-5, automatic), fonts-tlwg-loma:amd64 (1:0.6.4-2, automatic), acpi-support:amd64 (0.142, automatic), brltty:amd64 (5.5-4ubuntu2, automatic), ibus-table:amd64 (1.9.14-3, automatic), fonts-tlwg-waree-ttf:amd64 (1:0.6.4-2, automatic), libproxy1-plugin-networkmanager:amd64 (0.4.15-1, automatic), fonts-tlwg-garuda-ttf:amd64 (1:0.6.4-2, automatic), fonts-tlwg-sawasdee-ttf:amd64 (1:0.6.4-2, automatic), nautilus-sendto:amd64 (3.8.6-2, automatic), libgnome-games-support-common:amd64 (1.4.1-1, automatic), libgnome-games-support-1-3:amd64 (1.4.1-1, automatic), fonts-tlwg-typo-ttf:amd64 (1:0.6.4-2, automatic), avahi-autoipd:amd64 (0.7-3.1ubuntu1, automatic), libsane-hpaio:amd64 (3.17.10+repack0-5, automatic), fonts-tlwg-loma-ttf:amd64 (1:0.6.4-2, automatic), fonts-khmeros-core:amd64 (5.0-7ubuntu1, automatic), apport-gtk:amd64 (2.20.9-0ubuntu7, automatic), fwupd:amd64 (1.0.6-2, automatic), transmission-gtk:amd64 (2.92-3ubuntu2, automatic), fonts-tlwg-mono-ttf:amd64 (1:0.6.4-2, automatic), fonts-kacst:amd64 (2.01+mry-14, automatic), firefox:amd64 (59.0.2+build1-0ubuntu1, automatic), gnome-mines:amd64 (1:3.28.0-1, automatic), fonts-tlwg-typist-ttf:amd64 (1:0.6.4-2, automatic), fonts-sil-padauk:amd64 (3.003-1, automatic), pppconfig:amd64 (2.3.23, automatic), language-selector-gnome:amd64 (0.188, automatic), plymouth-theme-ubuntu-logo:amd64 (0.9.3-1ubuntu7, automatic), ubuntu-web-launchers:amd64 (18.04.5, automatic), fwupdate-signed:amd64 (1.18+10-3, automatic), python3-reportlab:amd64 (3.4.0-3build1, automatic), printer-driver-ptouch:amd64 (1.4.2-3, automatic), liblcms2-utils:amd64 (2.9-1, automatic), network-manager-pptp-gnome:amd64 (1.2.6-1, automatic), pcmciautils:amd64 (018-8build1, automatic), fonts-tlwg-umpush-ttf:amd64 (1:0.6.4-2, automatic), fonts-tlwg-laksaman-ttf:amd64 (1:0.6.4-2, automatic), printer-driver-foo2zjs-common:amd64 (20170320dfsg0-4, automatic), printer-driver-brlaser:amd64 (4-1, automatic)
End-Date: 2018-04-30 14:15:40