BeforeQuery + Search

Hi,

I have the below additional Where condition in my List page under BeforeQuery:

$strWhereClause="grant_period1='".$_SESSION["current_period"]."'";
This works fine and the listed is correctly filtered.
However, the Search does not work anymore. If I comment out the above line, Search works just fine.
Is this the way it is meant to work? If so, could you offer some advice on how you could have both working in tandem?
Many thanks in advance.

p.s. - I am using build #16275