Running multiple AsyncTasks at the same time — not possible?

I’m trying to run two AsyncTasks at the same time. (Platform is Android 1.5, HTC Hero.)
However, only the first gets executed. Here’s a simple snippet to describe my problem:

public class AndroidJunk extends Activity {
 class PrinterTask extends AsyncTask<String, Void, Void> {
     protected Void doInBackground(String ... x) {
      while (true) {
       System.out.println(x[0]);
       try {
        Thread.sleep(1000);
       } catch (InterruptedException ie) {
        ie.printStackTrace();
       }
      }
        }
    };

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        new PrinterTask().execute("bar bar bar");
        new PrinterTask().execute("foo foo foo");

        System.out.println("onCreate() is done.");
    }
}

The output I expect is:

onCreate() is done.
bar bar bar
foo foo foo
bar bar bar
foo foo foo

And so on. However, what I get is:

onCreate() is done.
bar bar bar
bar bar bar
bar bar bar

The second AsyncTask never gets executed. If I change the order of the execute() statements, only the foo task will produce output.

Am I missing something obvious here and/or doing something stupid? Is it not possible to run two AsyncTasks at the same time?

Edit: I realized the phone in question runs Android 1.5, I updated the problem descr. accordingly. I don’t have this problem with an HTC Hero running Android 2.1. Hmmm …