Your Power Transfer Switch defaults to connecting Shore Power to the Coach 117VAC load. With no shore power connected, when you start the Ginny and bring it "on-line" by turning the Ginny breaker on, the Power Transfer Switch senses this change and transfers the 117VAC Coach load to the Genny. Be very careful troubleshooting the Power Transfer Switch......LETHAL voltages are present.
When you get a chance to dance, or sit this one out......I hope you DANCE!
98 National Tradewinds 7370, powered by a 3126B 300HP CAT Turbo, Freightliner XC chassis