This is not really a problem. Your unit is not designed to draw enough current to supply both microwave and AC. You will need to turn off the AC while using the microwave. This also applies to appliances like toasters and electric griddles.
Just read elsewhere that someone had problem tripping circuit while running water heater, AC, and Microwave. Basically exceeding the 30 amps of the main breaker. I was utilizing the electric water heater switch to save propane.