Comment 0 for bug 1756187

This is due to some change in the gnome settings. Icon themes can inherit
from other themes. If an icon is still missing then the "hicolor" theme is
checked. However, Gtk+2 and Gtk+3 both also do some undocumented checks.

Gtk+3 is hardcoded to check "Adwaita" and "gnome". "gnome" is where those
missing icons are. But we are not using Gtk+3 yet.

Gtk+2 checks a xsetting called /Net/FallbackIconTheme. This is not set on
either my 16.04 system or my 18.04 system, yet my 16.04 system can find the
missing icons in "gnome". 18.04 however cannot. Setting this key (in
xfce4-settings-editor) fixes the problem. I have not yet figured out why
this was not necessary in 16.04.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: xubuntu-desktop 2.223
ProcVersionSignature: Ubuntu 4.15.0-12.13-generic 4.15.7
Uname: Linux 4.15.0-12-generic x86_64
ApportVersion: 2.20.8-0ubuntu10
Architecture: amd64
Date: Thu Mar 15 21:41:54 2018
InstallationDate: Installed on 2018-03-15 (0 days ago)
InstallationMedia: Xubuntu 18.04 LTS "Bionic Beaver" - Alpha amd64 (20180315)
SourcePackage: xubuntu-meta
UpgradeStatus: No upgrade log present (probably fresh install)