[development] Possible security issue in Drupal with previous/next thread in forum

Dear all, I hope that this is the right place to post. My issue http://drupal.org/node/559424 was closed with a "Wron't fix" answer. On my server, a query returns 21000 rows in 7412 ms. Just to be able to display previous and next forum thread. The number of rows seems too large. I double-checked on my testing server with 650.000 posts and the devel module + pgadmin3. Kind regards, Jean-Michel