Observable buffer losing items when onNext called in another thread

gistfile1.txt

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import rx.subjects.PublishSubject;


/**
 * BufferMissingTest.java
 * mln-feed-processing-feed-loading
 * 
 * Created by jeremy on Apr 18, 2014
 * DoApp, Inc. owns and reserves all rights to the intellectual
 * property and design of the following application.
 *
 * Copyright 2014 - All rights reserved.  Created by DoApp, Inc.
 */

/**
 * @author jeremy
 *
 */
public class BufferMissingTest {

  public static AtomicInteger createdCount = new AtomicInteger(0);
  public static AtomicInteger scheduledCount = new AtomicInteger(0);
  public static AtomicInteger scheduledAfterCount = new AtomicInteger(0);
  public static AtomicInteger firstSubjectCount = new AtomicInteger(0);
  public static AtomicInteger firstSubjectBufferCount = new AtomicInteger(0);

  public static void main(String[] args) throws InterruptedException {
    ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(100);
    PublishSubject<Integer> firstSubject = PublishSubject.create();
    firstSubject.buffer(100, TimeUnit.MILLISECONDS, 10).subscribe(list -> {
      firstSubjectBufferCount.addAndGet(list.size());
    });

    firstSubject.subscribe(i -> firstSubjectCount.incrementAndGet());

    Executors.newScheduledThreadPool(1).scheduleAtFixedRate(() -> {
      for (int i = 0; i < 8000; ++i) {
        final int j = i;
        createdCount.incrementAndGet();
        scheduler.schedule(() -> {
          scheduledCount.incrementAndGet();
          firstSubject.onNext(j);
          scheduledAfterCount.incrementAndGet();
        }, 10, TimeUnit.MILLISECONDS);
      }
      try {
        Thread.sleep(5000);
      } catch (Exception e) {}
    }, 0, 10, TimeUnit.SECONDS);

    while (true) {
      System.out.println("**************** " + System.currentTimeMillis() + " *******************");
      System.out.println("Created: " + createdCount);
      System.out.println("ScheduledCount: " + scheduledCount);
      System.out.println("ScheduledAfterCount: " + scheduledAfterCount);
      System.out.println("FirstSubject: " + firstSubjectCount);
      System.out.println("FirstSubjectBuffer: " + firstSubjectBufferCount);
      Thread.sleep(5000);
    }
  }
}