understanding agenda-group in drools

I tried a sample example to see how agenda-group works. Initially I set the focus of ksession to agenda-group "ag1" and fired the rules.

package com.sample

import com.sample.DroolsTest.Message;

rule "Hello World"
  agenda-group "ag1"
    when
        m : Message( status == Message.HELLO, myMessage : message )
    then
        System.out.println( "Hello World" ); 
        m.setMessage( "Goodbye cruel world" );
        m.setStatus( Message.GOODBYE );
        update( m );
end

rule "Hello World 2"
  agenda-group "ag2"
    when
        m : Message( status == Message.HELLO, myMessage : message )
    then
        System.out.println( "Hello World 2" ); 
        m.setMessage( "Goodbye cruel world" );
        m.setStatus( Message.GOODBYE );
        update( m );
end

rule "GoodBye"
  agenda-group "ag1"
    when
        m : Message( status == Message.GOODBYE, myMessage : message )
    then
        System.out.println( "GoodBye" );
        drools.setFocus("ag2");
        System.out.println("comeon man");
        m.setStatus(com.sample.DroolsTest.Message.HELLO);
        update(m);
end

rule "GoodBye 2"
  agenda-group "ag2"
    when
        Message( status == Message.GOODBYE, myMessage : message )
    then
        System.out.println( "GoodBye 2" );
end

This is the output I got.

Hello World
GoodBye
comeon man
Hello World 2
GoodBye 2
GoodBye
comeon man
Hello World 2
GoodBye 2
GoodBye
comeon man
Hello World 2
GoodBye 2
GoodBye
comeon man
Hello World 2
GoodBye 2
GoodBye
comeon man
Hello World 2
...
...

I could understand the first 5 lines of the output till "GoodBye 2". But since the focus was set to "ag2", how did it go back to "ag1" agenda-group's "GoodBye" rule and hence recursed.

Thanks.