node-base64 bug ? https://github.com/pkrumins/node-base64/

test-base64.js

var base64 = require('base64');
var assert = require('assert');

function roundTrip(str) {
  assert.equal(base64.decode(base64.encode(new Buffer(str, 'utf8'))), str);
}

['Hello', 'États-Unis'].forEach(roundTrip);