Searchable custom fields within a given range doesn't work!

Searchable custom fields within a given range doesn't work!
If I set a custom field (Number) for all Memberships, and if I add a certain value into that field to any existing contact, then if I make that field searchable for a given range, the search itself is useless and it doesn't work. Try it yourself! I think this is a bug.

I was using this search:
http://demo.civicrm.org/drupal/civicrm/member/search/basic?reset=1

That search doesn't work properly... I also tried to search for all "Presidents". See what happens: duplicate search results. Results should be the same as those ones from the regular Advanced Search, but they're not.