Durozone DynaFresh turns on when room exhaust fan switch turned on. Normal?

I have a hybrid heat-pump/electric furnace in my home for heating and cooling. It also has a Durozone Dyna-Fresh 35220/35221 unit on it to bring fresh air in on a timer. The system is about 20 years old. I've determined that the DynaFresh is wired up to the room's exhaust fan, so that whenever it is operating, the damper is opened, the furnace fan runs, and the room exhaust fan runs. Which is exactly what is described in the operating & wiring sheet.

However, the Dyna-Fresh unit is also activated whenever just the wall switch for the room exhaust fan is turned on. There is no mention of this behavior in the manual. We run the exhaust fan a lot, because it is in an area with cat litter boxes, and we want to keep the smell down. But this means that the furnace fan is also running all the time.

Is this normal & expected, or should I have it inspected?

Thanks

source https://hvac-talk.com/vbb/threads/2228302-Durozone-DynaFresh-turns-on-when-room-exhaust-fan-switch-turned-on-Normal?goto=newpost