I installed MATE desktop on a vanilla Ubuntu 18.04 installation that had been upgraded from 16.04, using
apt install ubuntu-mate-core ubuntu-mate-desktop (as per the instructions on wiki.mate-desktop.org/download#ubuntu), because the Mutiny panel layout provides my favorite user experience on a Linux desktop (along with the sadly defunct Unity).
I can apply the Mutiny layout using MATE Tweak, but after a reboot the icons on the top panel appear duplicated, as per the screenshot below:
Additionally, when I press the
Super (Windows) key and the HUD is displayed, it doesn't disappear after I click an icon nor if I press the key again, it just stays like this:
Additionally, if I use a keyboart shortcut - for example, I use
Ctrl+R to open a terminal and
Super+E for file explorer - the corresponding app is launched twice.
This also happens if I reset the panel layout (e.g. by switching to something like Netbook and then back to Mutiny) and then logout and login.
I removed MATE Desktop using
sudo apt remove --purge --autoremove ubuntu-mate-* mate-*, rebooted, then
apt update and
sudo apt-get install ubuntu-mate-desktop^, to reinstall as per @N0rbert's suggestion in the comments. However, after rebooting the desktop still has duplicated items (screenshot below). If I use Mate Tweak to change the layout to Mutiny, it displays fine, but after logging out and back in the panel icons are duplicated again.
dconf reset -f /org/mate/ as suggested, then used MATE Tweak to set the layout to Mutiny, and everything looked fine until I logout/login or reboot, after which the panel icons are duplicated, as shown below: