If like me you have replaced FreeNX by X2Go to remotely connect to your Desktop, and you use Mate as a fallback, you might have noticed that sometimes your machine becomes unresponsive. There is a bug/feature in the Mate settings daemon that detects the numlock status and seems to do it a bit too aggressively ( see bug 402 in X2go bug tracker
To avoid the behaviour, you can run the following command
gsettings set org.mate.peripherals-keyboard remember-numlock-state false
It disables the numlock status check avoid coming back to an unresponsive machine.