Ohh, my copy/paste technique was bad.
What I really meant was; Try moving the sense pins to PB3 and PB4.
CapacitiveSensor cs_4_2 = CapacitiveSensor(PB3,PB4);
If you are using 0 and 1 you are interferring with MISO, which is used by KnockBang, and gives the weird results and errors.
I tried your sketch wirth this change and the output is OK.