Mao sent more than two million soldiers to help NK fight during the Korean War. 400,000 young men died and thousands injured. So whether NK is sharing same ideology or depending on China for food, energy or raw materials, they better be grateful and show respect to its giant neighbour.
Many people even in China itself were angry that China seems to be providing everything to the North Koreans and wonder why China owed the North Koreans anything.
The fact was that Kim Ill Sung assisted and fought side by side with Mao and the chinese against Japan for almost a decade both in Korea and inside China, sacrificing huge resources and hundred of thousands of North Korean lives to the chinese resisitance against Japan in Northern China. Kim also has many of his family members killed inside China fighting the Japanese together with the chinese.
This fact is almost non existance in world history so very little ppl knew about it.
I think the US and the west are trying to break this bond by trying to cast a wedge between China and the North Koreans through deliberate"news' of North Korean disrespect for China or Kim Jong-Ill mistrust of China and China anger with the North. If one observed the Chinese and North Koreans knew such strategies and generally ignored it.