I don’t think the Chinese really mind the North Koreans having a few nukes for regime security, but the brinkmanship and continual threats against neighboring countries and the lack of Chinese style economic reforms is what I think is really causing the Chinese to snub Kim Jong-un:
North Korean leader Kim Jong-un may not be able to visit China on his first foreign trip if there is no progress in diplomatic efforts to persuade the North to give up its nuclear ambitions, South Korea’s ambassador to China said Wednesday.
Amb. Kwon Young-se was also cautious when talking about the possibility of a visit by Kim to Russia in May, saying it is too early to conclude that Kim’s trip to Russia would take place.
Kim took the helm of the authoritarian state in late 2011 after his father, Kim Jong-il, died. China is North Korea’s ideological ally and economic lifeline, but their political ties remain strained, particularly after the North’s third nuclear test in early 2013.
Russia has said that Kim would be among those attending the May 9th ceremony marking the 70th anniversary of the Soviet victory over Nazi Germany in World War II.
“I believe that a visit by Kim Jong-un to China is connected to the issue of denuclearization,” Kwon told Yonhap News Agency in an interview.
“From the perspective of China, there is a clear aspect that it would be burdensome to conduct a highest-level exchange with North Korea at a time when North Korea shows no progress in the nuclear issue,” Kwon said. [Yonhap]
You can read more at the link, but with that all said the Chinese are not about to abandon the regime to collapse either. They are just not providing as much to the regime as before and the regime may think buddying up to Putin may make up for the economic aid they have lost from the Chinese.