I incline to the opinion that the Japanese government has kept on lying.
English translation of a Japanese article: Gendai Net – October 10, 2012 –
The Senkaku Islands: Do They Belong to China?
Here Comes Trouble. “Official Document” of Foreign Ministry
Astonishing descriptions about the complicated Senkaku Island issue exist in official document of Foreign Ministry.
Foreign Ministry releases on its website “Japan Diplomatic Documents Digital Archives Vol. 18.” The documents exchanged between Count Ariake Yamagata, then Interior Minister, and Count Kaoru Inoue, then Foreign Minister have been released there. In the documents appears the phrase “Kumeakashima, Kubajima and Uotsurijima scattered between Okinawa Prefecture and China under the Manchus ……..,” which is descriptions over the Senkaku islands.
“Interestingly, on page 575 there is a description dated October 21, 1885 about construction of national signpost on the Senkaku islands planned by Japan at that time. Therein Foreign Minister Inoue says, ‘These islands are near the border of the Qing dynasty and the dynasty also gives a name to the islands. Recently the Qing dynasty’s newspapers have carried rumors that our country is going to occupy the islands belonging to the Qing dynasty located near Taiwan, and urged the Qing government to take precautions. At this time if we openly take measures such as constructing the signs of the Japanese nation, it is sure to invite suspicion of the Qing dynasty. We should wait for another chance to construct the signs of the nation and start clearing new land’ (Summary). This can be interpreted as Meiji government’s compromise after recognizing China’s connection to the Senkaku islands.” (Journalist covering diplomacy)
In the near future, China might use this diplomatic document to kick up a row. It’s really annoying.