NodeJS + Mongoose , 'unique' field attribute not working?

Question

I am making sure that my db doesnt have duplicate usernames or email addresses for my users using the unique: true attribute, but I am able to create users with duplicate usernames...so something isn't working. I have tried dropping the database, this did not solve the issue. Also in Model.on('index'), sometimes the error is not outputted to the console, sometimes it is. Strange.

var userSchema = mongoose.Schema({
    username: {type: String, unique: true, required: true},
    password: {type: String, required: true, select: false},
    emailAddress: {type: String, unique: true, required: true},
    emailVerified: {type: Boolean, default: false},
    emailVerificationCode: {type: Number},
    friends: []
});

userSchema.pre('save', function(next) {

    var user = this;

    if (!user.isModified('password')) return next();

    bcrypt.genSalt(10, function(err, salt) {

        if (err) return next(err);

        bcrypt.hash(user.password, salt, function(err, hash) {

            if (err) return next(err);

            user.password = hash;
            next();
        });

    });

});
var User = mongoose.model('User', userSchema);

User.on('index', function(err) { 
    console.log(err); 
});

module.exports = User;

And my node router for adding users to the db...

router.post('/register', function(req, res, next) {

    var newUser = new User({ username: req.body.username, password: req.body.password, emailAddress: req.body.email });

    newUser.save(function(err, newUser) {
        if (err) return next(err);

        newUser.sendVerificationEmail(function(err, isSent) {
            if (err) return next(err);
            res.json({ success: true });
        });

    });

});