Widget is breaking on filter function

I have created a widget which displays posts based on Display Posts shortcode. All works fine till I have added filter to public function widget() to output titles only (and need to be executed only for that widget):

    function display_posts_shortcode_clean_output( $output, $atts, $image, $title, $date, $excerpt, $inner_wrapper ) {
        $output = $title;
        return $output;
    } 
    add_filter( 'display_posts_shortcode_output', 'display_posts_shortcode_clean_output', 10, 9 );

When I will use that widget on the page once all is OK. When twice, with different widget control option widget code is breaking on function display_posts_shortcode_clean_output.

Do I need to move

add_filter( 'display_posts_shortcode_output', 'display_posts_shortcode_clean_output', 10, 9 );

to function __construct() and then from public function widget() call apply_filters? But in that case where should display_posts_shortcode_clean_output() function go?

Any clue?