Propane bad for the engine?

I have a Westinghouse Wgen7500DF dual fuel portable generator. Approximately every 3 months , I hook up a propane tank and run it for about 15 minutes since we almost never have power outages anymore. My neighbor just told me that I should use gasoline instead because he says always running it on propane is bad for the engine. Is he correct?

Edit: Thank you everyone for all your answers! There's a lot of knowledgeable people in sub. Appreciate all your responses!