Prueba este codigo, revisalo y intentalo en el changed del SLE
string ls_filter
long ll_length
If this.text <> '' Then
ll_length = len(this.text)
ls_filter = "left( string(campo_del_datawindow) ," + string(ll_length)+ ") = '" + this.text + "'"
Dw_1.SetFilter( ls_filter )
Else
Dw_1.SetFilter( "" )
End If
Dw_1.Filter()