View handler filter "views_handler_filter_fields_compare" not work

Hi,

I create a view has 2 fields then I add filter "fields comparison" (views_handler_filter_fields_compare) to it. But this does not affect the query.
I found that function add_where_expression() not work when 3rd arg is empty.

$this->query->add_where_expression($this->options['group'], $snippet);

But I change the line to below, it works.

$this->query->add_where_expression($this->options['group'], $snippet.' AND :val', array(
      ':val'=>1,
));