Since yesterday Alt+F4 is working unexpectedly on my computer. When I press those keys TTY4 is opened. Also, the application which is running on the GUI receives the Alt+F4 message. This is solved by rebooting the system, but after a while it starts doing this again.
I am running Ubuntu Gnome 16.10, Kernel version 4.8.0-39-generic and GNOME Shell version 3.20.4.