Let me tell you what I did now. It seems like the problem persists.
1 - I've created a new page in xowiki, inserted it in the search_observer_queue table and then I ran the search::indexer. I couldn't find the page in the search with the package_id.
2 - So I ran the ::xowiki::fix_all_package_ids procedure to create the package_id, did all the index stuff again and the search worked for me.
3 - To be sure about the issue I've created another page and looked for it in the acs_objects table. The page doesn't have the package_id for my xowiki instance. The other ones, for wich I had used the ::xowiki::fix_all_package_ids procedure have the package_id for my xowiki instance stored.
My conclusion is that the package_id is not being stored for new pages. Do I have to schedule the ::xowiki::fix_all_package_ids to run everytime I create a new page in xowiki? Can you tell me wich package is responsible for the bug?