For example in coin catalogue.
I select an issuer (Afghanistan) and I select ruling authority “Unidentified”. The system return 37 results.
Then, I remove the issuer (with the clear option, “x”, in the select box), keep the filter “Ruling authority: Unidentified” and click on “Search”. The system return 30340 results (from Afghanistan, Albania, Algeria...).

If I do not select an issuer, the ruling authority has not an option “Unidentified”.
