sean markham, thank you for reporting this and helping make Ubuntu
better.
As per below, when checking to see what happens when removing the
package adwaita-icon-theme, apt warns it will remove core packages
required for a desktop environment. Hence, this issue isn't a bug, but
an instance of "I shot myself in the foot".
sudo apt-get remove adwaita-icon-theme
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
bolt ca-certificates-java chromium-codecs-ffmpeg-extra default-jre-headless
fonts-dejavu-extra geoclue geoclue-ubuntu-geoip gir1.2-goa-1.0
gir1.2-snapd-1 gnome-applets-data gnome-flashback-common gnome-panel-data
gnome-themes-extra gnome-themes-extra-data gtk2-engines-pixbuf
indicator-common indicator-datetime indicator-keyboard indicator-messages
indicator-power indicator-session indicator-sound java-common
libaccounts-glib0 libactivation-java libapache-pom-java
libatinject-jsr330-api-java libatk-wrapper-java libatk-wrapper-java-jni
libbcmail-java libbcpkix-java libbcprov-java libcairo-gobject-perl
libcommons-io-java libcommons-lang3-java libcommons-parent-java libcpufreq0
libept1.5.0 libfcitx-gclient1 libfcitx-utils0 libfontawesomefx-java
libfontbox2-java libgeoclue0 libgeronimo-validation-1.0-spec-java
libgettext-commons-java libgif7 libglib-object-introspection-perl
libhibernate-validator-java libimgscalr-java libjackson2-core-java
libjackson2-jr-java libjboss-logging-java liblightdm-gobject-1-0
liblogback-java libmail-java libmetadata-extractor-java libsambox-java
libsejda-eventstudio-java libsejda-injector-java libsejda-io-java
libsejda-java libslf4j-java libsysmetrics1 libtwelvemonkeys-java
liburl-dispatcher1 libxmpcore-java metacity-common openjdk-11-jre-headless
openjdk-8-jre-headless python-cairo python-gobject-2 ubuntu-touch-sounds
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
libutempter0 lubuntu-icon-theme xterm
Suggested packages:
xfonts-cyrillic
The following packages will be REMOVED:
adwaita-icon-theme alacarte apport-gtk apturl caribou chromium-browser
chromium-browser-l10n default-jre deja-dup eog evince evolution-data-server
file-roller gdm3 gedit ghex gir1.2-caribou-1.0 gir1.2-clutter-1.0
gir1.2-gcr-3 gir1.2-gnomebluetooth-1.0 gir1.2-gnomedesktop-3.0
gir1.2-gtk-3.0 gir1.2-gtksource-3.0 gir1.2-gweather-3.0 gir1.2-mutter-1
gir1.2-mutter-2 gir1.2-nma-1.0 gir1.2-nmgtk-1.0 gir1.2-peas-1.0
gir1.2-rb-3.0 gir1.2-totem-1.0 gir1.2-vte-2.91 gir1.2-webkit2-4.0
gir1.2-wnck-3.0 gjs gmountiso gnome-applets gnome-bluetooth gnome-calculator
gnome-characters gnome-control-center gnome-flashback
gnome-getting-started-docs gnome-initial-setup gnome-panel
gnome-power-manager gnome-screensaver gnome-session-flashback
gnome-settings-daemon gnome-shell gnome-software gnome-software-plugin-snap
gnome-startup-applications gnome-system-monitor gnome-terminal gnome-todo
gnome-tweak-tool gnome-tweaks gnome-user-docs gnome-user-guide gnumeric-doc
gparted gstreamer1.0-clutter-3.0 humanity-icon-theme ibus ibus-gtk3
ibus-table indicator-applet-complete indicator-application
indicator-bluetooth indicator-printers isomaster language-selector-gnome
libappindicator3-1 libavahi-ui-gtk3-0 libcanberra-gtk3-module libcaribou0
libcheese-gtk25 libcheese8 libclutter-1.0-0 libclutter-gst-3.0-0
libclutter-gtk-1.0-0 libcolord-gtk1 libedataserverui-1.2-1
libedataserverui-1.2-2 libevdocument3-4 libevview3-3 libgail-3-0
libgail-common libgail18 libgjs0g libglade2-0 libgnome-bluetooth13
libgspell-1-1 libgtk-3-bin libgtk2-perl libgtk2.0-0 libgtk2.0-bin
libgtk3-perl libgtkhex-3-0 libgtkmm-2.4-1v5 libgtkmm-3.0-1v5
libgtksourceview-3.0-1 libgucharmap-2-90-7 libgweather-3-15 libido3-0.1-0
libindicator3-7 libmetacity1 libmutter-2-0 libnautilus-extension1a libnma0
libopenjfx-java libopenjfx-jni libpanel-applet3 libpeas-1.0-0
libreoffice-avmedia-backend-gstreamer libreoffice-gnome libreoffice-gtk3
librhythmbox-core10 libtotem0 libvte-2.91-0 libwnck-3-0 libyelp0
light-themes metacity mutter nautilus nautilus-extension-gnome-terminal
nautilus-share network-manager-gnome network-manager-pptp-gnome
notification-daemon openjdk-11-jre openjdk-8-jre openjfx orca pdfsam
python-glade2 python-gtk2 python3-aptdaemon.gtk3widgets
qt5-gtk-platformtheme remmina remmina-plugin-rdp remmina-plugin-secret
remmina-plugin-vnc seahorse software-properties-gtk synaptic
system-config-printer system-config-printer-common ubuntu-artwork
ubuntu-desktop ubuntu-docs ubuntu-mono ubuntu-release-upgrader-gtk
ubuntu-session ubuntu-software update-manager update-notifier
usb-creator-gtk yelp zenity
The following NEW packages will be installed:
libutempter0 lubuntu-icon-theme xterm
0 upgraded, 3 newly installed, 162 to remove and 0 not upgraded.
Need to get 3,111 kB of archives.