search filter – return select menu(s) to default state after submit

Hi,

I added a search filter in the sidebar of this test site.
http://dimenovels.discover-wp.com/
Custom field relationship is set to "OR".
When I select an Author and click Apply, I see the correct results page. But the Select menu doesn't refresh, so when I then select a Reviewer and click Apply, I see results for the Reviewer and the previously chosen Author. How can I make the Select menus return to their auto_fill_default state upon form submit?

Thanks!