Mamba 25 strange behaviour - very strange

[wallot]

Got my new futaba FASST radio and futaba recommends 6V for the reciever so i plugged in one of my small UBEC units and the MAMBA powers on right after I plug in the battery no matter in which position the on/off switch is. the switch works as without UBEC it behaves normally.

i have same wiring as in emaxx and Quark has no problems with it and powers only ig i switch the switch to ON. (servo works all the time as UBEC supplies the power to reciever)

only the signal and ground wires go from mamba to reciever

some evil magic. i can of course put on/off switch between reciever and UBEC but this is very strange. what gives signal to mamba to power on?