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.