strange behaviour when filtering a datagrid with a checkbox field

We have tested in versions 2.0.2 and 2.5.a2

We have a datagrid with a checkbox field that we add with:
DGridProyectos.setCellTemplate(new AW.Templates.Checkbox, 0);

In our test the datagrid presents five records, three of them have the string 'org' in the field 'Promotor'. When we filter the datagrid searching for those records that have the string 'org' in the field 'Promotor' and refresh the datagrid it presents the three records and two lines more with no data but the checkbox.

¿Anybody knows if this is a misfunctionallity or something we our doing wrong?

Thanks in advance.

Maybe you need grid.setRowCount(3)