oooooooooooh, 5V single ended control lines next to a 3 phase motor. NOISE. First make your software react to input only if it is the same for at least 100 mSec. The second thing to try, which will not upset your design too much is to connect 100 ohms from +5 to the port pin, a .1 uF capacitor to ground and the switch between the pin and ground and a mammoth capacitor (100uF tantalum minimum) from the +5 side of the resistor to ground.