China (PRC) is a different case - if a government official discovers you have multiple passports, even by accident, they will force you to make a decision on the spot.
Interesting. Although, if you had say a UK and Chinese passport, and you told them 'I want to keep the Chinese one' and they 'remove' your UK passport, you're still a UK citizen. Unless they just revoke the Chinese citizenship on the spot, which would work.