Why can "sub2" retrieve the first item of "src1"?

SubscribeLater.java

package hoge;

import rx.*;
import rx.schedulers.*;

import java.util.concurrent.TimeUnit;

// See the items in backpressure bufffer will be genereated
// for the observer who subscribed later?
public class SubscribeLater {
    public static void doIt() {
        Scheduler sched = Schedulers.newThread();
            
        Observable<Long> src1 =  
            Observable.interval(1, TimeUnit.MILLISECONDS).
            onBackpressureBuffer();

        src1.
            observeOn(sched).
            subscribe(
                       s -> {
                           if (s % 10000 == 0) {
                           System.out.println("Sub 1: " +s);
                           }
                           if (false) { // Just drop them!
                           try {
                               Thread.sleep(1000);  // Blocks
                           } catch (Exception ex) {
                           }
                           }
                       },
                       throwable -> {System.err.println(throwable);},
                       () -> {System.out.println("complete");}
                       );
        try {
            Thread.sleep(10000);
        } catch (Exception ex) {
        }

        // Which item will this show?
        src1.
            subscribe(
                      s -> {
                          System.out.println("Sub 2: " +s);
                      });

        try {
            Thread.sleep(10000);
        } catch (Exception ex) {
        }

    }
}