The remote operates a relay on the control panel which is near the battery box and also a short run to the slide pump motor. The inside switch has a much longer circuit loop. Direct current is a lazy form of electricity and doesn't like to travel long distances relative to the wire size and current load. I noticed our trailer does the same thing, although its fairly slight. You can notice it but you have to be paying attention. My crackpot theory is the circuit length is the cause.
---- Relative to some of my theories, this one is pretty good.