Of course I know about mainland.
Despite of all the development, to be honest, it still better to be Taiwanese than mainlander. More undeveloped, poorer, lack of culture, bad society, etc.
That because you asked them in China and you tell them you are mainlander. Of course they will politely answer it. It's different at behind. But even at worst they will not condemn mainlander so badly either, they just very concern because you are Chinese too.
People can actually tell the different between mainlander and Taiwanese. Even taxi driver in China know you came from Taiwan. Body language, fashion style, dialect, and face.