I remember having used this gesture, but my current customization generates a Ctrl-Shift-Alt instead.
I looked for a mention about some option that should be selected in order to make it work but I found nothing of the sort. Maybe someone who has not customize this gesture will have some explanation...
Could it be the Toggle Numlock Internally
option from the second tab of the Global Feature Selector
The only reason why I don't use nice feature is that I found an even better way to switch from one mode to another