Problem with JDO pagination

Question

I have a unit test that populates the datastore with 26 entities. I have a DAO that tries to retrieve these entities and page through them but somehow I can't get it to work entirely. If I do query.setRange(0,10) it works but not for query.setRange(10,20). The query returns 0 results even if the unit test shows that I have 26 entities.

public void testGetModulesWithPagination(){  
 String current_user="currentUser";
 String tags[] = {"football","soccer"};

 for (int i=0;i<=25;i++){
  Module m = new Module();
  m.setOwner("myName");
  m.setObjective("m"+i+" objective");
  m.setTitle("m"+i);
  m.setTags(tags);
  dao.insert(m);
 }
 Query query = new Query(Module.class.getSimpleName());
 List<Module> modules_page_one = dao.getModules(current_user,"football", "1");
 List<Module> modules_page_two = dao.getModules(current_user,"football","2");

 assertEquals(26, DatastoreServiceFactory.getDatastoreService().prepare(query).countEntities());
 assertNotNull(modules_page_one);
 assertEquals(10,modules_page_one.size());
 assertNotNull(modules_page_two);
 assertEquals(10,modules_page_two.size()); //FAILS here
 assertFalse(modules_page_one.equals(modules_page_two));
}

This is my dao implementation

public List<Module> getModules(String owner,String tag,String page){
 getPm();
 String queryString = "select from "+Module.class.getName()+" where owner!='"+owner
  +"'";
 Query query = pm.newQuery(queryString);

 Long pageNumber = Long.parseLong(page);
 Long lower_bound = pageNumber*10-10;
 Long upper_bound = pageNumber*10;

 log.info("pageNumber "+pageNumber);
 log.info("lower_bound "+lower_bound);
 log.info("upper_bound "+upper_bound);

 query.setRange(lower_bound, upper_bound);
 List<Module> modules = (List<Module>) pm.detachCopyAll((List<Module>) query.execute());
 log.info("modules results size "+modules.size());
 log.info(modules+"");
 List<Module> search_results = new ArrayList<Module>();
 for (Module module:modules){
  String module_tags[] = module.getTags();
  for (int i=0;i<module_tags.length;i++){
   if (module_tags[i].equals(tag)){
    search_results.add(module);
    continue;
   }
  }
 }
 closePm();
 return search_results;
}