Alt+Left Arrow turns screen black

I have Ubuntu Gnome 16.04 installed and every time I press Alt+Left Arrow to go up a directory in my file browser or back a page in my web browser my screen turns all black and there is a terminal cell. Once I press it Alt+Left Arrow again I go to the login screen. Why is this happening and how do I fix this? Any help would be appreciated.

Update: I added an additional tag because it is known to happen in 18.04 too.

There is an open issue about this:

https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1508146

A solution that worked for me was to run:

sudo kbd_mode -s

I just had a problem very close to this one. Without changing any keyboard settings, Alt + ← begun to take me directly to the graphical login screen. Alt + → took me to the full screen terminal login.
After a couple of weeks, Alt + Tab also stopped working. That was too much, and I started to study the problem. I noticed in the keyboard settings that Alt + Tab had been changed to Super + Tab (not by me). When I changed it back, also the Alt + Arrow behavior went back to normal.