I am not sure about MultiWii, but it does need an external receiver, or not?
If so, the failsafe values are sent to the receiver at bind time (when signal is usually good). When the receiver looses signal, it will give out the programmed failsafe values (say THR=-100%, AIL=ELE=RUDD=0) - the MultiWii still gets a regular input.
Maybe your receiver has a feature to give nothing out when it looses the connection to the transmitter. I have seen only those who continue to give out the last signal or the programmed failsafe values.
