Well it looks like the U.S. government is carrying on "discussions" with the North Koreans and the only way that anyone knew about it was from the work of amateur observers who watch flights in and out of U.S. military installations.
From the article...
Senior U.S. administration officials held secret talks in North Korea on at least three occasions in 2011 and 2012, The Asahi Shimbun has learned.
Although the visits had potential implications for Japan, Washington did not inform its security partner at the time and only informally confirmed one of them when the Japanese side pressed, government and other sources in Japan, South Korea and the United States said.
The article goes on to say that when the Japanese complained, the administration said that questions about this threatened bilateral relations.