Vows callbacks drop arguments after error

gistfile1.js

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

function doSomethingAsync(callback) {
	var err = null;
	var testValue = 'a';

	process.nextTick(function() {
		callback(err, testValue);
	});
}

function doSomethingAsyncWithError(callback) {
	var err = true;
	var testValue = 'a';

	process.nextTick(function() {
		callback(err, testValue);
	});
}


vows.describe('simple-async-error').addBatch({

	'Generate success response to async function': {
		topic: function() {
			doSomethingAsync(this.callback)
		},
		'Validate success': function(err, testValue) {
			assert.ok(!err);
		},
		'Validate testValue': function(err, testValue) {
			assert.equal(testValue, 'a');
		}
	},

	'Generate error response to async function': {
		topic: function() {
			doSomethingAsyncWithError(this.callback)
		},
		'Validate error': function(err, testValue) {
			assert.ok(err);
		},
		'Validate testValue': function(err, testValue) {
			// This assertion fails. It shouldn't.
			assert.equal(testValue, 'a');
		}
	}

}).run();