I have noticed something opposite of that.
Every now and then when opening a project a new instance of a driver, other than the one I selected, would appear on forms other than the Main Form (EthernetIPforCLXCom).
Not a big deal since I just delete it, but your case is different.
Just checked v3.96 and Page2 already has ModbusRTUCom1 driver on it.
Wild guess, Archie was doing some testing with it and left it there.