The NPM global flag seems to be inconsistent on Windows

Runnin from the console

> npm root -g

Or programmatically

var npm = require("npm");
npm.load(null, function (err, npm) {
    npm.config.set("global", true);
    npm.root;
});

I get a different results on Windows. The first one returns C:\Users\myuser\AppData\Roaming\npm\node_modules and the second one C:\Program Files (x86)\nodejs\node_modules. The same happens when I install a module, doing this programmatically tries to install it on program files instead of AppData.

Could this be a bug? Or am I doing something wrong?

On linux it works consistently. I've not tried on Mac.

Update: I tried this on Mac and it works fine.