Help in setting Search Page

Hi,
I tried to setting search page to display the newest coupon but it is impossible
Go to Theme Setup => Page setup => Search page
– I chose Default Order By = Date (newest first) => Not work
– I chose Default Order By = System Set (no default order) => Not work
– I turn on “Show Sort By Options” and chose Default Order By = Date (newest first) => Not work
– I turn on “Show Sort By Options” and add Custom Sort By Options = [orderby=date&order=asc] => Not work

I tried many option but it is impossible. Hope that someone can help me.
NOTE: This happens when I add a coupon and change the publish time
Ex: Today, I add a coupon but I changed the publish time to June 15th, 2015. This coupon still be displayed first while there are many other coupons added today.

Thank you very much!