This is usually because the MIDI out and MIDI in of the Nova is connected to a sequencer which is remapping Bank/Program messages (generated by changing Program/Bank on a Part) to a channel corresponding to the Global channel of the Nova. The solution is to Filter out Bank messages in the Sequencer, or disconnect the midi out of the Nova, or disable the 'Thru' function on the sequencer, or to change the Global channel of the Nova to one not being used in the sequencer.