neo4j concurrency issue?

neo4j-error.js

// create some nodes
var node1 = db.createNode();
var node2 = db.createNode();

// save them in parallel (works fine)
async.parallel([
  function (cb) { node1.save(cb) },
  function (cb) { node2.save(cb) }
], function (err) {
  if (err) {
    console.log(err);
  } else {
  
    // if both finish saving, try to 
    // simultaneously create relationships 
    // between the two nodes, one in each direction
    async.parallel([
      function (cb) { node1.createRelationshipTo(node2, 'KNOWS', {}, cb) },
      function (cb) { node2.createRelationshipTo(node1, 'KNOWS', {}, cb) }
    ], function (err) {
      if (err) {

        // this is where it goes bad
        console.log("no worky", err);
      } else {
        console.log("it worked");
      }
    });
  }
});