My old RV does not have an automatic transfer - I have to plug my shore cable manually into my generator socket to have gen power and clearly then it can't also be plugged into shore power, and vice versa.
But with a new-fangled ATS system, surely these people who have designed these things have isolated the systems so that if you're plugged into shore power AND your generator is also turned on that the ATS system can handle this situation safely and appropriately?!?!?
This would seem to be a fundamental part of any such design. You wouldn't want to try to apply double voltage to the RV and you wouldn't want your genset trying to back-feed the shore.
Steve