I went to Thai immigration and checked. I needed my Thai visa in my new passport to apply for a Chinese visa. Chinese rule. Thai immigration didn't want to do it at first as it's not necessary. I then explained about the Chinese regulations. You must have a current visa for the country you are applying FROM in you current passport. Australian going to China from Thailand. Same going to UK and Nigeria carry old and new passports, no problems at all. I travel a lot.