They include territorial arguments over Cho Haku Zan (Korean: Paek Tu San), a mountain located on the border between North Korea and China. It is holy to the Korean people but the Chinese up until recently have paid very little attention.
Also, there is the Kogurye Theories and the mysterious motives between why the Chinese Government-sponsored Historical Committee would want to start bringing this up now. The Kogurye Theory states that the Ancient Korean nation of Kogurye was actually just a Chinese Province.
The Kogurye Theories, by extension, would mean that most of the Korean Peninsula even Pyongyang and Seoul are actually rightful historical possessions of the Chinese. All of a sudden bringing this up now could mean that growing China is positioning herself to move into and occupy starving North Korea if and when it does collapse.