Why are 4 circuits connected to a single switch?
I will copy this as an answer as I believe it is most probable.
You may be detecting phantom voltage.
I have seen 2 circuits crossed in the field but never 4.
The chances of this are very remote. Read up on phantom voltage and you might find why you detect voltage. For them to be connected all 4 would have to be odd or even breakers.
if some are odd and some are even it will be phantom voltage because if connected odd and even would be a direct short. There is a possibility of a back feed through a 240v device but this would be as rare as all 4 actually being connected in the field. So the most probable answer is phantom voltage.