I think the issue is in the way you have set the DataAssist search up to use the checkboxes.
when you select to Use Checkbox search criteria type, you will need to specify the Checked and Unchecked values to use.
With the other search criteria types, they will not be included if there is no value, but with the checkbox search criteria type, they will be included and use the unchecked value you set.
see the attached screen shot for more details
Most likely, for your needs, you would want to use the edit criteria type, even for the check boxes.