Okay, so I did this under keymod, but I played the east asia map with 5 civs (Tokugawa (Me), Qin Shi Huang, Wang Kon, Genghis Khan, and I can't spell the Khemr leader name). I went into the worldbuilder at the beginning and moved everyone to more accurate places. So I played the game isolated in Japan and the only contact I had was Korea. And I did nothing bad to Wang Kon, it was just green all the way down and he was friendly. Eventually I sent scouts and met everyone else.
I keep playing blah blah blah blah and eventually I have friendly Wang Kon, cautious Genghis Khan, Annoyed Qin Shi Huang and annoyed Khmer. And suddenly, Wang Kon and Khmer declare war on me. I figure okay, maybe this happens time to time. I make peace afterwards Wang Kon is still friendly with me. I make a defensive pact with him and as soon as that expires because Qin Shi Huang declares war on Wang Kon, they do it again. And Wang Kon was still friendly. WHAT'S GOING ON!???
I keep playing blah blah blah blah and eventually I have friendly Wang Kon, cautious Genghis Khan, Annoyed Qin Shi Huang and annoyed Khmer. And suddenly, Wang Kon and Khmer declare war on me. I figure okay, maybe this happens time to time. I make peace afterwards Wang Kon is still friendly with me. I make a defensive pact with him and as soon as that expires because Qin Shi Huang declares war on Wang Kon, they do it again. And Wang Kon was still friendly. WHAT'S GOING ON!???