I was playing Hearts of Iron IV, all DLC enabled and updated, as Ironman Romania. I am having a good game as Fascist Romania and was fun. I am in the Axis faction with Germany and we are at war with Czechoslovakia, France, Greece, etc as well as Japan and Mengukuo. The last two are important. I am playing and I then see that for some reason the "Join the Axis" decision has become available after a while. I think to myself and decide to just go with it and press the button. Then, to my dismay, Legionary Romania has joined the Greater East Asian Co-Prosperity Sphere. What the hell. I went to war with the German Reich and the rest of the Axis and am no longer at war with the Japanese. I think this is a very cringe bug due to it ruining my Ironman save game.