I have a double entry visa for China. I've used up the first one and will reenter China for the second one in the next few days.
Now I'd really like to go to Taiwan by ferry but was worried that it would use up my last entry into China and I'd then have to fly out of Taiwan.
But then I started thinking that since China doesn't recognize Taiwan that from their point of view I would not be leaving China, so it should not use up an entry, so I could return and continue travelling in China.
But since the China/Taiwan situation is pretty special and unique there could also be special rules about it.