Intent and getSerializableExtra value return

In onCreate I get an extra serializable from intent into itemsList of my activity

itemsList = (ArrayList<HashMap<String, String>>) intent
  .getSerializableExtra("sliding_menu_content");

then in the activity I add some other map elements to the itemsList array. My surprise is that, changing the orientation of the device, getSerializableExtra returns the updated state of itemsList including all map elements additions. How is it possible?