mongoose: populate option limit - not working

code below gives 2 friends instead of 1.

var opts = { path: ‘author.friends’, select: ‘name’, options: { limit: 1 } }

  var assert = require('assert')
  var mongoose = require('mongoose');
  var Schema = mongoose.Schema;
  var ObjectId = mongoose.Types.ObjectId;

  /**
   * Connect to the db
   */

  var dbname = 'testing_populateAdInfinitum_1'
  mongoose.connect('localhost', dbname);
  mongoose.connection.on('error', function() {
    console.error('connection error', arguments);
  });

  /**
   * Schemas
   */

  var user = new Schema({
    name: String,
    friends: [{
      type: Schema.ObjectId,
      ref: 'User'
    }]
  });
  var User = mongoose.model('User', user);

  var blogpost = Schema({
    title: String,
    tags: [String],
    author: {
      type: Schema.ObjectId,
      ref: 'User'
    }
  })
  var BlogPost = mongoose.model('BlogPost', blogpost);

  /**
   * example
   */

  mongoose.connection.on('open', function() {

    /**
     * Generate data
     */

    var userIds = [new ObjectId, new ObjectId, new ObjectId, new ObjectId];
    var users = [];

    users.push({
      _id: userIds[0],
      name: 'mary',
      friends: [userIds[1], userIds[2], userIds[3]]
    });
    users.push({
      _id: userIds[1],
      name: 'bob',
      friends: [userIds[0], userIds[2], userIds[3]]
    });
    users.push({
      _id: userIds[2],
      name: 'joe',
      friends: [userIds[0], userIds[1], userIds[3]]
    });
    users.push({
      _id: userIds[3],
      name: 'sally',
      friends: [userIds[0], userIds[1], userIds[2]]
    });

    User.create(users, function(err, docs) {
      assert.ifError(err);

      var blogposts = [];
      blogposts.push({
        title: 'blog 1',
        tags: ['fun', 'cool'],
        author: userIds[3]
      })
      blogposts.push({
        title: 'blog 2',
        tags: ['cool'],
        author: userIds[1]
      })
      blogposts.push({
        title: 'blog 3',
        tags: ['fun', 'odd'],
        author: userIds[2]
      })

      BlogPost.create(blogposts, function(err, docs) {
        assert.ifError(err);

        /**
         * Population
         */

        BlogPost
        .find({ tags: 'fun' })
        .lean()
        .populate('author')
        .exec(function(err, docs) {
          assert.ifError(err);

          /**
           * Populate the populated documents
           */

          var opts = {
            path: 'author.friends',
            select: 'name',
            options: { limit: 1 }
          }

          BlogPost.populate(docs, opts, function(err, docs) {
            assert.ifError(err);
            console.log('populated');
            var s = require('util').inspect(docs, { depth: null })
            console.log(s);
            done();
          })
        })
      })
    })
  });

  function done(err) {
    if (err) console.error(err.stack);
    mongoose.connection.db.dropDatabase(function() {
      mongoose.connection.close();
    });
  }