Exceptions to 6 months residence permit rule

Hello, I am a foreign national studying in Korea with my residence permit expiring end of August. I was planning to go to China end of May and stay there for a week. I am aware my permit expires in less than 6 months (it will be renewed but not before my planned trip to China) and this is a major problem, but I read somewhere that people who have been to China in the last two years and can still show the (expired) visa in their passport can get the visa anyway. Is that true? I have been to China this January.
Thank you for your reply.