I'm affected on Ubuntu 17.04 on a Thinkpad X230 with a German keyboard and en_CA as the system language.
Alt + Left showed me the gnome-shell lock screen. After successfully logging into the session again Alt + Up showed me my password plain text.
$ sudo kdb_mode -s
(as recommended by ahayzen) works for me too.
I'm affected on Ubuntu 17.04 on a Thinkpad X230 with a German keyboard and en_CA as the system language.
Alt + Left showed me the gnome-shell lock screen. After successfully logging into the session again Alt + Up showed me my password plain text.
$ sudo kdb_mode -s
(as recommended by ahayzen) works for me too.