Users have the ability to create smart queries using different types of filters and filter options, one of which is a 'one of' filter type option. When using multiple filter options of this type in a smart query users are finding that the first filter automatically adds a defaulted blank row which can cause inaccurate results if not seen and reset by users prior to running the query.
This is by design. This is happening because focus is being set on the first available field when the smart query opens. When you set focus on a grid with no editable rows, it creates a row for you to start typing/make a selection.