Arduino + XBox 360 RF module
Okay, so I've found out what the problem was all along. As I've said, I connected everything directly. Because of that, the Arduino pins will sometimes start picking up electrical noises and change state as described in tutorial about digital pins


  This also means however, that pins configured as pinMode(pin, INPUT) with nothing connected to them, or with wires connected to them that are not connected to other circuits, will report seemingly random changes in pin state, picking up electrical noise from the environment, or capacitively coupling the state of a nearby pin.


Thus adding a pullup resistor to each data pin resolved the problem.