I installed yarn with npm --global.
I'm on yarn 1.3.2.
Until now everything ok.
Now If I'm in a npm project (with package.json file in root) and try this command: yarn global upgrade-interactive it works ok but instead of writing the right package.json file in "C:\Users\John\AppData\Local\Yarn\config\global\package.json" it writes the one in my folder where I launch the command.
I think this is a dummy bug.