China admitted Diaoyu islands was Japan's territory, 1960 map

Japan has agreed to buy Senkaku islands, Diaoyu islands as known in China, disputed with China from their private owners, prompting an angry rebuke from China a day after Chinese President Hu Jintao warned against such an “illegal” move.

However, the communist sovereignty once admitted Diaoyu islands belonged to Japan! On the map published in 1960, Beijing obviously regarded Diaoyu islands/Senkaku islands as one part of Japan:

After that, oil was found around Diaoyu islands, now China regretted and wanted to claim her territory on these islands. From 1960-2012, just 52 years, and Chinese government always would like to use the words like "from the ancient time, Diaoyu islands have been the Chinese territory blur blur blur", is this kind of sarcastic?