Buster without environment does not execute both groups

browser-fail.js

buster.testCase('browserfail', {
    'it fails in the browser': function() {
        assert.isTrue(false);
    }
});

buster.js

var buster = require('buster');
var config = module.exports;
config['node tests'] = {
    environment: 'node',
    tests: [ 'node-fail.js' ]
};
config['browser tests'] = {
    environment: 'browser',
    tests: [ 'browser-fail.js' ]
};

node-fail.js

var buster = require('buster');
var assert = buster.assertions.assert;

buster.testCase('nodefail', {
    'it fails on node': function() {
        assert.isTrue(false);
    }
});