function get_terms_by_post_type($post_type,$taxonomy,$fields='all',$args){
    $q_args = array(
        'post_type' => (array)$post_type,
        'posts_per_page' => -1
    );
    $the_query = new WP_Query( $q_args );
    
    $terms = array();
    
    while ($the_query->have_posts()) { $the_query->the_post();
        
        global $post;
        
        $current_terms = get_the_terms( $post->ID, $taxonomy);
        
        foreach ($current_terms as $t){
          //avoid duplicates
            if (!in_array($t,$terms)){
                $terms[] = $t;
            }
        }
    }
    wp_reset_query();
    
    //return array of term objects
    if ($fields == "all")
        return $terms;
    //return array of term ID's
    if ($fields == "ID"){
        foreach ($terms as $t){
            $re[] = $t->term_id;
        }
        return $re;
    }
    //return array of term names
    if ($fields == "name"){
        foreach ($terms as $t){
            $re[] = $t->name;
        }
        return $re;
    }
    // get terms with get_terms arguments
    if ($fields == "get_terms"){
        $terms2 = get_terms( $taxonomy );
        
        //echo '<pre>';print_r($terms2);echo '</pre>';
        foreach ($terms as $t){
            if (in_array($t,$terms2)){
                $re[] = $t;
            }
        }
        return $re;
    }
}

function get_terms_by_post_type($post_type,$taxonomy,$fields='all',$args){
    $q_args = array(
        'post_type' => (array)$post_type,
        'posts_per_page' => -1
    );
    $the_query = new WP_Query( $q_args );
    
    $terms = array();
    
    while ($the_query->have_posts()) { $the_query->the_post();
        
        global $post;
        
        $current_terms = get_the_terms( $post->ID, $taxonomy);
        
        foreach ($current_terms as $t){
            //avoid duplicates
            if (!in_array($t,$terms)){
                $t->count = 1;
                $terms[] = $t;
            }else{
                $key = array_search($t, $terms);
                $terms[$key]->count = $terms[$key]->count + 1;
            }
        }
    }
    wp_reset_query();
    
    //return array of term objects
    if ($fields == "all")
        return $terms;
    //return array of term ID's
    if ($fields == "ID"){
        foreach ($terms as $t){
            $re[] = $t->term_id;
        }
        return $re;
    }
    //return array of term names
    if ($fields == "name"){
        foreach ($terms as $t){
            $re[] = $t->name;
        }
        return $re;
    }
    // get terms with get_terms arguments
    if ($fields == "get_terms"){
        $terms2 = get_terms( $taxonomy, $args );
        
        foreach ($terms as $t){
            if (in_array($t,$terms2)){
                $re[] = $t;
            }
        }
        return $re;
    }
}

EDIT: Added the fix(es). But somehow it's still not working for me. The count still shows the incorrect value.