neo4j rest api uniqueness not working?

I'm trying to create an unique node in neo4j, but can't make it work.

node code:

var node = db.createNode({sampleDataKey: "sampleDataValue"});

node.save(function (err, user) {

    node.index('user', 'indexValue', 'indexValue', function (err) {
        if (err) console.log(err);
        console.log(user.id);
    });
});

I'm using this node module: https://github.com/thingdom/node-neo4j

I have modified the Node.js from the neo4j lib. to:

else {

                                  var urlToPost = ((("" + services.node_index) + "/") + index + '?uniqueness=create_or_fail');
                                  console.log(urlToPost);
                                  console.log(key + ':' + value);

/*   123 */                       return __this._request.post({
/*   124 */                         url: urlToPost,

/*   125 */                         json: {
/*   126 */                           key: key,
/*   127 */                           value: value,
/*   128 */                           uri: __this.self
                                    }
                                  }, __cb(_, __frame, 17, 21, function ___(__0, __4) {
/*   123 */                         response = __4;
                                    console.log('response');
                                    __then();
                                  }, true));
                                }

Each time i execute the code a new new node is created, but after that errors. ... Here is the console log for 2 executions:

30 May 16:51:24 - [nodemon] starting `node app.js`
Express server listening on port 3000
http://localhost:7474/db/data/index/node/user?uniqueness=create_or_fail
indexValue:indexValue
response
338
30 May 16:55:38 - [nodemon] restarting due to changes...
30 May 16:55:38 - [nodemon] /Users/nikolaialeksandrenko/Documents/work/noject/app.js


30 May 16:55:38 - [nodemon] starting `node app.js`
Express server listening on port 3000
http://localhost:7474/db/data/index/node/user?uniqueness=create_or_fail
indexValue:indexValue
response
339