the default where clause is only used if 2 conditions are met:
1) A prior search has not been completed in the current browsing session
2) The trigger is not met
When you do a search, the search is stored in a session variable, the search in the session variable will be used if it exists and the trigger is not met.
In your case, using the Before Page Load trigger will cause the search code to run any time the page is loaded.
also in your case, the search is using the GET Method, not the POST methods, so the trigger Dave is using will not be valid.
On the bindings panel, make sure there is a URL Variable section that contains a binding for the Status querystring.
then in Data Assist Search, click the lightning bolt next to Trigger and select the Status URL Variable.
this way the search code will only trigger if that variable is present.
then set the default where to: