levelgraph level-sublevel approximateSize issue

index.js

(function() {
  var data, db, graph, graphSubLevel, level, levelgraph, levelup, otherSubLevel, search, sublevel;

  levelup = require('level');

  sublevel = require('level-sublevel');

  levelgraph = require('levelgraph');

  level = levelup('yourdb');

  db = sublevel(level);

  graphSubLevel = db.sublevel('graph');

  otherSubLevel = db.sublevel('other');

  graph = levelgraph(graphSubLevel);

  data = [
    {
      subject: 'matteo',
      predicate: 'friend',
      object: 'daniele'
    }, {
      subject: 'daniele',
      predicate: 'friend',
      object: 'matteo'
    }, {
      subject: 'daniele',
      predicate: 'friend',
      object: 'marco'
    }, {
      subject: 'lucio',
      predicate: 'friend',
      object: 'matteo'
    }, {
      subject: 'lucio',
      predicate: 'friend',
      object: 'marco'
    }, {
      subject: 'marco',
      predicate: 'friend',
      object: 'davide'
    }
  ];

  search = [
    {
      subject: 'matteo',
      predicate: 'friend',
      object: graph.v('x')
    }, {
      subject: graph.v('x'),
      predicate: 'friend',
      object: graph.v('y')
    }, {
      subject: graph.v('y'),
      predicate: 'friend',
      object: 'davide'
    }
  ];

  graph.put(data, function(error, result) {
    return graph.search(search, function(error, result) {
      if (error) {
        return console.error(error);
      } else {
        return console.log(result);
      }
    });
  });

}).call(this);

package.json

{
  "private": true,
  "dependencies": {
    "level": "^0.18.0",
    "level-sublevel": "^6.3.15",
    "levelgraph": "^0.9.1"
  },
  "scripts": {
    "test": "node index.js"
  }
}